Ovulation induction refers to the induction of ovulatory function of the ovary using pharmacological or surgical methods, usually with the aim of inducing the development, maturation and ovulation of a single follicle or a small number of follicles, and is mainly used to treat patients with ovulatory disorders leading to infertility. Ovulation disorders are one of the common factors leading to female infertility, mainly due to abnormalities in the hypothalamic-pituitary-ovarian axis. WHO classifies ovulation disorders into 3 types, type I is anovulation due to hypothalamic-pituitary abnormalities, patients usually have low estrogen and gonadotropins, i.e. FSH and LH, type II is non-hypothalamic-pituitary factors, most commonly polycystic ovary syndrome, which presents with estrogen in the normal range but often abnormally elevated LH/FSH values, type III presents with abnormally FSH and LH levels elevated and low estrogen levels, such as premature ovarian failure and gonadal dysgenesis. Ovulation induction therapy can be performed in patients with ovulation disorders of types I and II. In patients with normal menstruation and ovulation, during the late luteal phase of the previous menstrual cycle and the early follicular phase of the current cycle, a group of sinus follicles will enter the growth and developmental track together in the ovary under the action of follicle stimulating hormone (FSH) and the other follicles will be occluded, a process called recruitment. The growth of the follicles after recruitment is mainly dependent on gonadotropins, especially follicle stimulating hormone (FSH), and follicles can only continue to grow when FSH levels reach or exceed a certain threshold. The sensitivity of different follicles to FSH varies. Around day 5-7 of the menstrual cycle, the follicle with the lowest FSH threshold, i.e. the one most sensitive to FSH, will preferentially develop into the dominant follicle, while the other follicles will gradually atrophy. After the dominant follicle matures, the hypothalamus releases large amounts of gonadotropin-releasing hormone under the positive feedback effect of its high level of estrogen secretion on the hypothalamus, which forms the LH peak and thus initiates ovulation. According to the above principle, gonadotropin (Gn) is the key to induce ovulation, and currently medications are generally used to induce ovulation, and surgery is not recommended as a first-line treatment option. The commonly used clinical drugs to induce ovulation: oral clomiphene and letrozole mainly induce ovulation by promoting endogenous FSH secretion, while injectable urotropin, urinary follicle stimulating hormone and recombinant FSH promote follicle development by exogenous FSH. HCG, on the other hand, has a similar chemical structure and biological activity to LH, and is commonly used to stimulate the LH peak to induce follicular maturation and ovulation. For patients with infertility due to ovulation disorders, it is recommended to clarify the specific cause of ovulation disorders, induce ovulation, monitor follicle development with ultrasound and guide intercourse under the guidance of a professional reproductive physician.