Objective? To investigate the effects of letrozole on blood pulsatility index (PI), blood resistance index (RI), serum estradiol (E2), prolactin (PRL) and luteinizing hormone (LH), follicle stimulating hormone (FSH) levels in patients with polycystic ovary syndrome (PCOS). Methods The clinical data of 78 cases patients with PCOS treated in Ehu Branch of Wuxi Xishan People's Hospital from January 2019 to June 2020 were retrospectively analyzed. They were divided into the clomiphene group (treated with clomiphene 100 mg/d), the letrozole group A (treated with 2.5 mg/d letrozole on the basis of clomiphene group) and the letrozole group B (treated with 5.0 mg/d letrozole on the basis of clomiphene group) according to different treatment schemes, 26 cases in each group. The endometrial receptivity and sex hormone levels before and after treatment, ovulation and pregnancy after treatment, and the occurrence of adverse reactions during treatment of patients were compared among the three groups. Results Compared with before treatment, the endometrial thickness and serum FSH levels of patients in the three groups after treatment increased significantly, while the levels of RI, PI, and serum E2, PRL, LH after treatment decreased significantly; compared with the clomiphene group, the endometrial thickness, ovulation rate and serum FSH level of the patients in the letrozole A group and the letrozole B group after treatment increased significantly, and the letrozole B group was significantly higher than the letrozole A group; the RI, PI and serum E2, PRL and LH levels of the patients in the letrozole A group and the letrozole B group after treatment decreased significantly, and the letrozole B group was significantly lower than the letrozole A group; the total incidence of excellent pregnancy in the letrozole B group was significantly higher than that in the clomiphene group and the letrozole A group (allP<0.05); there was no significant difference in the total incidence of adverse reactions among the three groups (P>0.05). Conclusion Compared with clomiphene monotherapy, clomiphene combined with letrozole in the treatment of PCOS can effectively regulate sex hormone levels, improve endometrial receptivity of patients, so as to improve the ovulation rate and excellent pregnancy rate, and which has good safety, and the therapeutic effect of letrozole with 5.0 mg is more ideal.