Objective:To investigate the effects of letrozole combined with human menopausal gonadotropin (HMG) on pregnancy rate and prognosis in patients with refractory polycystic ovary syndrome (PCOS).Methods:A total of 102 patients with refractory PCOS who received treatment in Jinhua Hongyue Women's and Children's Hospital between May 2019 and May 2020 were included in this study. They were randomly assigned to observation and control groups ( n = 51/group). All patients received the same treatment in the early period. During later ovulation induction period, patients in the control group were administered HMG and those in the observation group were given letrozole combined with HMG. Before treatment and 3 months after treatment, sex hormones [follicle stimulating hormone (FSH), luteinizing hormone (LH), estradiol (E 2), testosterone (T)], arterial hemodynamic indicators around the follicle [end diastolic velocity (EDV), peak systolic velocity (PSV), pulsation index (PI)], endometrial thickness and classification were compared between the two groups. The ovulation rate and pregnancy rate as well as pregnancy outcomes at 6 months of follow-up were recorded in each group. Results:After 3 months of treatment, FSH, LH, E 2 and T levels in each group were significantly decreased compared with those before treatment (all P < 0.05). FSH, LH, E 2 and T levels in the observation group were (1.85 ± 0.45) U/L, (9.86 ± 1.47) U/L, (81.25 ± 10.47) pmol/L, (1.75 ± 0.26) nmol/L, respectively, which were significantly lower than those in the control group [(3.12 ± 1.47) U/L, (12.58 ± 2.14) U/L, (109.25 ± 27.14) pmol/L, (3.58 ± 0.76) nmol/L, t = 5.90, 7.48, 6.87, 16.27, all P < 0.05). EDV in each group was significantly decreased after 3 months of treatment compared with that before treatment (both P < 0.05). After treatment, EDV in the observation group was significantly lower than that in the control group [(3.12 ± 1.42) cm/s vs. (5.14 ± 1.89) cm/s, t = 21.14, P < 0.001]. PSV in each group was significantly increased after treatment compared with that before treatment (both P < 0.05). After treatment, PSV in the observation group was significantly higher than that in the control group [(13.36 ± 2.01) cm/s vs. (10.24 ± 2.47) cm/s, t = 4.21, P < 0.001]. In each group, PI measured after treatment was not significantly different from that measured before treatment (both P > 0.05). After treatment, endometrial thickness in the observation group was significantly higher than that in the control group [(9.09 ± 1.58) mm vs. (8.41 ± 1.42) mm, t = 2.28, P < 0.05]. Ovulation rate in the observation group was significantly higher than that in the control group [88.24% (45/51) vs. 70.59% (36/51), χ2 = 4.85, P < 0.05]. There were no significant differences in endometrial type, biochemical pregnancy, clinical pregnancy rate, abortion rate, and premature delivery rate between the two groups (all P > 0.05). Conclusion:Letrozole combined with HMG has an ideal effect on refractory PCOS. It can improve the levels of sex hormones, restore the hemodynamic status in ovarian stroma and increase ovulation rate.