Objective: The present study aimed to explore the D-Dimer cutoff values for predicting Pulmonary Thromboembolism after Cesarean Section. Methods: This study recruited 198 women after cesarean section with suspected PE symptoms in Women’s Hospital of Nanjing Medical University from January 2018 to December 2024. Among them, 33 patients who were diagnosed as PE by CTPA were divided intthe study group, and the 165 patients who were not diagnosed as PE by CTPA during the same period were divided into the control group. Analyze the age, Body Mass Index (BMI), gestational age at delivery (weeks)，number of fetuses, surgical indications, risk factors for VTE after delivery, D-dimer (mg/L) within postpartum 24 hours and the time of using LMWH after cesarean section. Draw the receiver operating characteristic curve (ROC) of D-dimer to determine the optimal sensitivity and specificity of the D-dimer value, with the area under the curve (AUC) used to evaluate the cut-off value. Analyze the risk factors for PE and calculate the odds ratio (OR) with a 95% confidence interval. Result: The D-dimer level in the PE group was (8.98 ± 6.91) mg/L, significantly higher than that in the non-PE group (4.03 ± 2.08) mg/L (P < 0.05), indicating that D-dimer is a strong predictor of PE and should be prioritized in clinical practice. The initiation of anticoagulation therapy in the PE group was delayed compared to the non-PE group, with a statistically significant difference, suggesting that early anticoagulation—when bleeding risk is low—plays a crucial role in preventing PE after cesarean delivery. The optimal cut-off value of D-dimer within 24 hours post-cesarean was 7.48 mg/L, with a specificity of 93.9% and sensitivity of 62.4%. The area under the curve (AUC) was 0.75 (95% CI: 0.652–0.848, P = 0.000), demonstrating significant diagnostic value for PE. When the D-dimer cut-off was adjusted to 1.59 mg/L, the 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), meaning that for every 1 mg/L increase in D-dimer, the risk of PE increased by 58%. Conclusion: This study conducted a preliminary exploration of the D-dimer cut-off value at 24 hours after cesarean delivery, aiming to establish a more convenient and safer screening method to improve the identification of postoperative PE. This approach could facilitate timely intervention and reduce unnecessary imaging examinations.