Abstract: Objective To explore the risk factors of pregnancy of frozen embryo transfer cycle. Methods Clinical data of 15 848 frozen embryo transfer cycles(15 848 patients with frozen embryo transfer)was retrospectively analyzed and pregnancy outcomes were tracked. According to different pregnancy outcomes, the patients were divided into pregnancy group(9 459 cases)and non-pregnancy group(6 389 cases). Clinical data such as age, infertility duration, type of infertility, estrogen level, endometrial preparation method, endometrial thickness on transplantation day were collected. Multivariate Logistic regression analysis was used to analyze the factors affecting pregnancy in frozen embryo transfer cycle. Results A total of 27 104 embryos/blastula were transferred in this group, with clinical pregnancy rate of 59.69%(9 459/15 848). Univariate analysis showed that age, embryo age, number of embryos/blastula transferred, and endometrium thickness on transplantation day were related to clinical pregnancy rate( P<0.01). Logistic regression analysis showed that age, endometrial thickness on transplantation day, number of embryos/blastula transferred, embryo age were risk factors affecting clinical pregnancy outcomes(P<0.05 or P<0.01). Conclusion Patients' age, endometrial thickness on transplantation day, number of embryos/blastula transferred, embryo age are influencing factors of clinical outcomes of frozen embryo transfer.