Objective To explore the effects of in vitro culture time of frozen cleavage embryo after thawing on clinical pregnancy rate during frozen-thawed embryo transfer (FET) cycles. Methods The clinical data of 692 patients were analyzed; they received FET in the Department of Reproductive Medicine Center, Changhai Hospital, Navy Medical University (Second Military Medical University) from January to December in 2016. According to the days of in vitro culture between thawing and transferring, the patients were divided into three groups:no in vitro culture group, 1-day in vitro culture group and 2-day in vitro culture group. The pregnancy outcomes were compared between the three groups. Results There were no significant differences in age, body mass index, infertile duration, basic follicle-stimulating hormone (FSH) level or endometrial preparation protocol between the three groups (all P>0.05). The embryo loss rates of the no in vitro culture group, the 1-day in vitro culture group and the 2-day in vitro culture group were 0.0% (0/706), 13.3% (64/481) and 43.0% (114/265), respectively, and the difference was statistically significant (P<0.01). There were no significant differences in number of transfered embryo or endometrial thickness on transplantation day between the three groups (both P>0.05). The good-quality embryo transfer rates in the 2-day in vitro culture group and 1-day in vitro culture group were significantly lower than that in the no in vitro culture group (both P<0.01), and the clinical pregnancy rate in the 2-day in vitro culture group was significantly higher than that in the no in vitro culture group (P<0.01). Conclusion In vitro culture for 1-2 days after thawing frozen cleavage embryos may increase the embryo loss rate, but it can improve the clinical pregnancy rate by screening the embryos with developmental potential.