Data show that about 10-15% of couples are infertile. With the change of society, the phenomenon of multiple abortions and late marriage and childbirth has increased, making the incidence of infertility has a tendency to increase. There are many factors that lead to infertility, and the pain caused by infertility is no less than the loss of a loved one, however, finding the cause of infertility is like finding a needle in a haystack, and many families face a lack of rational thinking about infertility, biased listening, indiscriminate treatment, paying a lot of energy and money, and even miss a good time for treatment. Before starting a fertility test, it is important to first make a proper assessment of whether infertility exists. Infertility is defined as a couple who have normal sexual intercourse without contraception for one year without pregnancy. Generally, infertility-related tests should be performed only after at least one year of unsuccessful attempts to conceive, but women over 35 years of age can start infertility counseling earlier if appropriate and begin with simple, non-invasive tests. At the first visit, it is best to go together as a couple and ask for a detailed medical history, such as family history, previous general health (history of tuberculosis, mumps, etc.), occupation, medication, history of miscarriage, menstruation, sexual life, etc., in order to detect important clues. The male partner accounts for 25-40% of the various factors of infertility. In the case of the male partner, after physical examination and external genital examination, semen analysis can be performed (2-5 days of abstinence). If semen is devoid of sperm, it should be checked for the presence of fructose in the semen to determine whether there is ejaculatory tract stenosis or congenital vas deficiency. The test can be repeated once after such conditions are ruled out, and if it still shows azoospermia or oligospermia, further hormone measurements can be performed. In some men, semen is not liquefied, there may be inflammation, poor lifestyle or stress that may influence the test, and in others, there are organic diseases that need to be treated accordingly. Sometimes a testicular biopsy may be performed when the true cause of infertility cannot be confirmed. In men with non-obstructive azoospermia or severe oligospermia, karyotyping should be recommended especially before the proposed assisted reproductive technology (e.g. ICSI). The female partner is the subject of the fertility event, and many aspects of fertility are female related, with female factors accounting for 40%-55% of all causes of infertility. A thorough history taking must be followed by a careful specialist examination, such as overflowing breast, sexual hair distribution, and genital examination. If there are abnormal findings, such as overflowing breast, inflammation of the genital tract, abnormal genital tract structures or tumors, the next step of diagnosis and treatment is required to address these abnormalities. For example, severe cervical inflammation can alter the cervical mucus properties thereby affecting sperm penetration and inactivating sperm, and artificial insemination may be considered if treatment is not effective. Some patients with severe inflammation of the reproductive tract should be tested for pathogenic microorganisms, especially for chlamydia, mycoplasma and gonorrhea, as these infectious factors can easily affect fertility. If there are no specific findings, ovulatory function and the degree of patency of the fallopian tubes, which are the main causes of female infertility, can be considered. Basal body temperature measurement is economical and non-invasive. Patients are instructed to take and record their temperature every morning before waking up by mouth table to find out whether it is monophasic or biphasic and whether there is a short luteal phase. If the menstrual disorder or basal temperature is monophasic, hormone levels must be measured. Sex hormones (at least the three major pituitary hormones, FSH, LH, and PRL) should be measured 3-5 days after menstruation to identify at which level of the hypothalamic-pituitary-ovarian axis the cause of the ovulatory abnormality is located. If the basal FSH level is high, decreased ovarian reserve function can be considered. However, if both primary amenorrhea or menstrual scarcity and dysmorphic features are present, karyotype analysis is required to rule out ovarian dysplasia or hypoplasticity due to Turner’S syndrome or hyperesthesia syndrome. In addition, thyroid function and adrenocortical function are also closely related to female fertility, and supplemental measurements of hormones such as TSH, 17-OHP and DHEAS are needed when necessary. Ultrasonography is useful both to detect organic pelvic problems and to monitor follicular development and ovulation. If the gonad is striated on ultrasound, the chromosome should be checked. If the karyotype is XY, the gonad should be removed to prevent malignant changes. In some women, the basal body temperature is biphasic and the mid-luteal blood progesterone measurement also shows ovulation, but in fact ovulation does not occur and only ultrasound can reveal that the egg has not been expelled (unruptured follicle luteinization syndrome). Usually, continuous ultrasound monitoring of follicular growth and ovulation is performed from day 10 of the menstrual cycle, and the test for pregnancy can be guided at the same time as the examination. In cases of normal follicular development and ovulation but failed pregnancy attempts, especially in those with a history of previous uterine manipulation or pelvic surgery, abnormal tubal patency is considered. HSG is only a screening test. If abnormalities are suspected (e.g. endometrial polyps, endometrial tuberculosis, uterine adhesions and longitudinal septum), laparoscopy or hysteroscopy should be performed to confirm the diagnosis. The corresponding corrective surgery will be performed. If the above tests do not reveal any problems, immune factor tests can be performed, especially in infertile couples with previous spontaneous abortions. The immune factor test is divided into sperm immune abnormalities and female fluid immune abnormalities. For example, anti-sperm antibodies can be produced by both men and women and can cause sperm agglutination, affect sperm motility and survival rate, and inhibit fertilization function. Anti-hyaline antibodies in the female partner can alter the zona pellucida properties and affect the fertilization process, while anti-cardiolipin antibodies can cause thrombosis in small blood vessels at the embryo implantation site, leading to implantation failure. Assisted reproductive technology may be considered for some of these abnormalities where conservative treatment has failed. In addition, endometriosis is very common in infertility patients, accounting for about 80%. The causes of infertility in patients with endometriosis are complex, with the influence of the pelvic and abdominal cavity microenvironment and immune abnormalities being the main factors, as well as abnormalities in tubal egg transport and ovarian function. However, many patients do not have symptoms such as dysmenorrhea or painful intercourse. For patients with unexplained infertility, laparoscopic examination can be performed if the condition is suspected, and laparoscopic surgery is feasible to determine the presence of lesions. In some cases of asymptomatic adenomyosis, vaginal ultrasound and MRI can be used as non-invasive diagnostic tools. Once diagnosed, treatment with GnRH analogues for 3-6 months, followed by aggressive attempts to conceive can improve the chances of conception. It should be noted that after a series of tests, more than 90% of infertile couples can find the cause, but there are still a few patients for whom no definite factor can be found, i.e., couples with unexplained infertility; or cases in which the infertility factor is treated and still unable to conceive. In this case, after full explanation, the patient should be allowed to relax and rest, and there are cases of unexpected natural conception. In conclusion, infertility is related to a very large number of links, complex and diverse etiologies, and numerous corresponding examination methods and means. The steps of easy and non-invasive tests should be followed first, and invasive and expensive tests second. Some basic tests are necessary for every infertile couple, while others should be performed specifically for initial abnormal findings. Infertility often involves more than two factors and must be evaluated in a comprehensive manner for both men and women.