Objective To evaluate the role of transvaginal color Doppler ultrasound measurements of endometrial thickness,endometrium and subendometrial blood distribution patterns and flow index in predicting endometrial receptivity and pregnancy outcome of freezing embryo transfer(FET).Methods 468 cycles FET were analysed retrospectively.Endometrial thickness,endometrium and subendometrial blood distribution patterns,pulsatility index (PI),resistance index (RI),systolic /diastolic ratio (S/D) of endometrial and subendometrial blood flows with transvaginal ultrasonography were measured on the day of progesterone initiation.Based on the clinical pregnancy or not,patients were divided into two groups.The comparison of these indicators were carried out between pregnant group and non pregnant group.Results The endometrium and subendometrial blood distribution patterns had statistical difference between the two groups(P ＜0.05),the clinical pregnancy rate of Ⅰ,Ⅱ,Ⅲ blood distribution patterns were 31.0％,62.5％,79.0％ respectively.In the pregnancy group,the S/D,PI,and RI of endometrium were significantly lower than those in the nonpregnant group (P ＜ 0.05),and there was no significant difference between the pregnant group and nonpregnant group in endometrial thickness(P ＞0.05).Conclusions Endometrium and subendometrial blood distribution patterns and flow index measured with transvaginal color Doppler ultrasound could assess endometrial receptivity and guide the time selecting of FET transplantation.