Objective：To explore the new D-dimer cutoff values after cesarean section as a predictive factor for pulmonary embolism （PE）. Methods：A total of 198 women with suspected PE after cesarean section who delivered at the Women’s Hospital Affiliated to Nanjing Medical University from January 1，2018，to December 31，2024，were selected for a retrospective case - control study. 33 patients were finally diagnosed with PE by computed tomographic pulmonary angiography（CTPA）and were included in the study group，while 165 patients were excluded from having PE by CTPA and were included in the control group. Analyze the age，body mass index（BMI），gestational age at delivery（weeks），number of fetuses，surgical indications，risk factors for venous thromboembolism （VTE）after delivery，D-dimer concenrtration within postpartum 24 h，and the time of using LMWH after cesarean section. The receiver operating characteristic（ROC）curve of D-dimer was plotted to determine the optimal sensitivity and specificity of the D-dimer value， and the area under the curve（AUC）was used to evaluate the cutoff value. The risk factors for PE were analyzed，and the odds ratio（OR） and 95% confidence interval were calculated. Results：The D - dimer level in the PE group was 6.82（4.46，13.06）mg/L，significantly higher than that in the non-PE group 3.83（2.35，5.21）mg/L（P ＜ 0.01），and the anticoagulation initiation time after surgery in the PE group was later than that in the non-PE group[1（0，3）d vs. 2（1，5）d，P ＜ 0.05]. The optimal cut-off value of D-dimer within 24 h post - cesarean was 7.48 mg/L，with a specificity of 93.9% and sensitivity of 62.4%. The AUC was 0.75（95% CI：0.652-0.848，P ＜ 0.001）. When the D-dimer cut-off was adjusted to 1.59 mg/L，its sensitivity and specificity were 100% and 43.2%，respectively，with the highest Youden index for negative predictive value. This threshold may be particularly meaningful for early PE screening after cesarean delivery. Prolonged immobilization and D-dimer levels were identified as two independent risk factors for PE. Notably ， D - dimer was a continuous risk factor（OR=1.58）. Conclusion：D - dimer within 24 h after cesarean section is a continuous and independent risk factor for PE and a strong predictive indicator. It can be used as a more convenient and safe screening method to identify PE after cesarean section，so as to intervene in time and reduce unnecessary imaging examinations.