Objective To study the influence of densification degree and quantity of D4 embryos on clinical pregnancy outcome in the freezing and thawing embryo transfer cycle，and to make clear the effect of densification embryo on live birth rate. Methods Younger patients（< 40 years old）having frozen ⁃thawed embryo transfer were selected. According to the densification degree of transferred embryos，the transfer cycles were divided into group A （containing two more partially densified embryos or densified embryos）；group B（containing one partially densified or densified embryo group）；group C（without partially densified or densified embryos）. The implantation rate and clinical outcome were analyzed，and the final pregnancy outcome of densified embryos was studied. Results （1）Age and body mass index in group C were significantly lower than those in group A. Infertility duration，basic FSH，basic LH，and basic E2 were not significantly different among the three groups by using nonparametric test. There was no statistical difference among the three groups in the endometrial preparation protocols. The endometrial thickness of group C was significantly higher than that of group A.（2）The average number of high ⁃quality embryos transferred in group A，B and C decreased successively，and the difference was statistically significant. The loss rate of early pregnancy was significantly different among the three groups，which was increased in group B but decreased in group A. The live birth rate was significantly different among the three groups，and the difference between group A and group B and C was significant. Conclusion Transferring two more partially densified embryos can significantly increase live birth rate，but not increase multiple pregnancy rate and cesarean section rate. However，transferring one more partially densified embryo could not improve the clinical pregnancy rate，multiple pregnancy rate and live birth rate.