Letrozole tablets have certain ovulation-promoting effects and are aromatase inhibitors, which were mainly used in the treatment of breast cancer in the past. At present, letrozole is mainly used in patients with clomiphene resistance, and its possibility of inducing ovulation is about 80%. It is mostly applied after the beginning of menstrual cycle or after the withdrawal of luteinizing hormone bleeding, and is applied on the 3rd-7th day of menstruation for 5 days.