Women present with left-sided pain in the lower abdomen, which is clinically indicated by the presence of pain in the left lower abdomen. Firstly, consider that the patient has gynecological problems, commonly ovulation pain, left adnexitis, pelvic inflammatory disease or ectopic pregnancy. Secondly, consider that the patient has gastrointestinal diseases, such as ulcerative colitis, etc.: I. Gynecological diseases: 1. Ovulation pain: some sensitive women will have ovulation pain, or ovulation bleeding. Most of them belong to physiological pain. After the follicle enters the abdominal cavity, the follicular fluid stimulates the peritoneum with abdominal pain. It may also be due to inflammation or adhesions around the ovaries and fallopian tubes, when there is also pain in the left lower abdomen during ovulation; 2. Left adnexitis: adnexitis is inflammation of the fallopian tubes and ovaries due to infection by pathogens. It is caused by infection of the upper reproductive tract of women and mainly includes endometritis, tubal inflammation, tubo-ovarian abscess and pelvic peritonitis. The inflammation may be limited to one area or may involve several areas at the same time. Therefore, there may be left lower abdominal pain that is persistent and worsens after activity or after intercourse. It is accompanied by abnormal vaginal discharge, as well as abnormal vaginal bleeding. 4. Ectopic pregnancy: It refers to the fertilized egg that is laid outside the body cavity of the uterus due to reproductive system diseases or injuries, also known as ectopic pregnancy. When the blood is confined to the lesion area, the main manifestation is pain in the lower abdomen, including the left lower abdomen. In addition, patients tend to have menopause and vaginal bleeding as the main symptoms. Second, gastrointestinal diseases: mainly ulcerative colitis, which is an inflammatory lesion of the colon caused by a variety of causes, and can be caused by bacteria, protozoa and other organisms, or by metabolic reactions and physicochemical factors. It is mostly associated with mild or moderate abdominal pain, which is vague in the left lower abdomen or lower abdomen, and may also develop into full abdominal pain. Patients are advised to go to the hospital for timely examination to exclude the possibility of tumors or other malignant diseases in the pelvic cavity and to identify the cause to facilitate targeted treatment.