Objective: To explore the best time for progesterone supplementation in AID ovulation induction cycles by Letrozole. Methods: The data analysed in this study were collected from 509 patients who were performed AID (Artificial Insemination by Donor) administrated letrozole (LE) between 2014.8-2015.7. All patients were randomly divided into 4 groups by the time of progesterone administrated, including experimental group and the control group. The experimental group was divided into group 1-72 h after ovulation, group 2-48 h after ovulation, group 3-24 h after ovulation and control group—without administrated LE. The gestation and live birth rate were evaluated by monitoring vaginal ultrasound and HCG blood value 14 d after AID. Results: The pregnancy rate with administrated progesterone added 72 h after ovulation was 31.9%, which was significantly higher than those of other groups, the same situation as groups added progesterone was significantly higher than the control group. However, there was no significant difference in the numbers of abortions among the four groups. The LBR of group 4 was significantly lower than that of group 1. Conclutions: Progesterone administrated 72 h after ovulation can promoted the gestation rate, but did not affect the rate of miscarrage .