Abstract: Objective To explore the effect of metformin combined with different doses of clomiphene in the treatment of PCOS.Methods The data of PCOS patients from August 2015 to April 2018 in our hospital were retrospectively analyzed. Research group and control group were treated with metformin combined with clomiphene citrate 100 mg and metformin combined with clomiphene citrate 50 mg, respectively. The level of serum LH and E₂, mature follicles and endometrial thickness on the day of hCG administration, ovulation rate, pregnancy rate and early spontaneous abortion rate were compared between research group and control group.Results There were 218 and 240 patients in research group and control group, respectively. There were no significant difference in serum LH and endometrial thickness on the day of hCG administration and early spontaneous abortion rate (P>0.05). The serum E₂ on the day of hCG administration, mature follicles, ovulation rate, and clinical pregnancy rate was significantly higher in research group than those in control group (P<0.05).Conclusion Using metformin combined with clomiphene citrate 100 mg to treat PCOS patients can significantly increase the level ofserum E₂ on the day of hCG administration, mature follicles, ovulation rate, and clinical pregnancy rate.