To investigate the diagnostic value of blood flow parameters of uterine artery and vascularization parameters of scar site for cesarean scar pregnancy (CSP) of women during the first trimester of pregnancy. Methods: 82 women with CSP during the first trimester of pregnancy (≤12 gestational weeks) who had caesarean section history from June 2018 to June 2020 were selected in group A retrospectively，114 normal pregnant who had caesarean section history during the first trimester of pregnancy were selected in group B，and 74 normal pregnant women with vaginal delivery history and without caesarean section history were selected in group C. The values of uterine artery blood flow parameters, such as pulsatility index (PI)，uterine artery resistance index (RI), peak systolic velocity/end diastolic velocity (S/D), of the women in the three groups were examined by transvaginal color Doppler ultrasound. The vascularization parameters of scar site, such as vascularization index (VI)，blood flow index (FI), and vascularization flow index (VFI), of the women in the three groups were examined by the three-dimensional energy Doppler ultrasound mode combined with Vocal software. Receiver operator characteristic (ROC) curve was used to analyze the diagnostic value of the vascularization parameters of scar site for CSP. Results: There was significant difference in the RI value of the uterine artery blood flow parameters of the women among the three groups, and there was significant difference in the S/D value of the uterine artery blood flow parameters of the women between group A and group C. There were significant differences in the values of VI, FI, and VFI of vascularization parameters of scar site of the women between group A and group B (all P<0.05). The area under the curve (AUC) of the VI value, the FI value, and the VFI value of the women for diagnosing CSP was 0.768, 0.795, and 0.805, respectively, and the detection critical value of which were 8.49, 20.93, and 2.27, respectively. Conclusion: The values of RI and S/D of uterine artery of the pregnant women with different delivery history during the first trimester of pregnancy are differences, and the values of VI, FI, and VFI of uterine artery examined by three-dimensional energy Doppler ultrasound for diagnosing CSP of the women have certain values. In order to improve the accuracy of diagnosing CSP during the first trimester of pregnancy, the quantitatively analysis should be done based on the critical value of the RI and S/D values of uterine artery of the pregnant women with different delivery history in clinic.