Objective：To investigate the risk factors for gestational diabetes mellitus（GDM） in polycystic ovary syndrome（PCOS） at different gestation，and to further understand the clinical characteristics of PCOS complicated with GDM. Methods：Pregnant women diagnosed with PCOS in the Obstetrics and Gynecology Department of Maternal and Child Health Care Family Planning Service Center of Shapingba District of Chongqing and received standard treatment and prenatal care services during March 2013 to March 2015 were included. According to the result of oral glucose tolerance test at 24th week and 32nd week of gestation，aforementioned pregnant women were divided into GDM group（n=20 at 24 weeks of gestation，n=28 at 32 weeks of gestation） and Non-GDM group（n=77 at 24 weeks of gestation，n=69 at 32 weeks of gestation）. Their basic information and the differences in the level of androgen and insulin in each group were compared，and the risk factors for GDM were analysed. Results：At 24th week of gestation，there were significant differences in the weight gain and level of insulin between GDM group and Non-GDM group [the weight gain in GDM group is （5.54±1.32） kg，while in Non-GDM group is （4.08±0.91） kg，t=2.487，P=0.015；the concentration of insulin in GDM group is （30.35±8.70） pmol/L，while in Non-GDM group is （25.47±7.56） pmol/L，t=3.289，P=0.001]. At 32nd week of gestation，there were significant differences in the weight gain，family history of diabetes，the level of testosterone and insulin between GDM group and Non-GDM group [the weight gain in GDM group is （9.83±0.91） kg，while in Non-GDM group is （8.61±1.23） kg，t=2.283，P=0.025；patients with family history of diabetes in GDM group are 10 cases，while in Non-GDM group are 9 cases， ?字2=3.939，P=0.0４７；the concentration of testosterone in GDM group is （3.49±1.65） nmol/L，while in Non-GDM group is （2.46±1.17） nmol/L，t=2.542，P=0.013；the concentration of insulin in GDM group is （33.78±7.01） pmol/L，while in Non-GDM group is （27.12±6.39） pmol/L，t=4.108，P=0.000]. Logistics regression analysis showed that both the higher weight gain and level of insulin were independent risk factors for GDM in PCOS pregnant women（OR=2.467，95%CI=1.912 to 3.355，P=0.029；OR=1.565，95%CI=1.287 to 1.921，P=0.007） at 24th week of gestation；while the higher weight gain and level of testosterone and insulin were independent risk factors for GDM in PCOS pregnant women（OR=2.640，95%CI=2.392 to 3.588，P=0.033；OR=1.587，95%CI=1.103 to 3.307，P=0.045；OR=2.735，95%CI=1.182 to 4.803，P=0.001） at 32nd week of gestation. Conclusions：Higher weight gain and level of insulin are risk factors for GDM in PCOS pregnant women at second trimester and third trimester. Furthermore，higher level of testosterone is a risk factor for GDM in PCOS pregnant women at third trimester.