Objective: To evaluate the incidence of postoperative venous thromboembolism (VTE) after thoracic surgery and its characteristic. Methods: This was a single-center, prospective cohort study. Patients undergoing major thoracic surgeries between July 2016 and March 2017 at Department of Thoracic Surgery, Beijing Chaoyang Hospital Affiliated to Capital Medical University were enrolled in this study. Besides the routine examination, all patients were screened for deep venous thrombosis (DVT) by using noninvasive duplex lower-extremity ultrasonography after surgery. CT pulmonary angiography (CTPA) was carried out if patients had one of the following conditions including typical symptoms of PE, high Caprini score (>9 points) or new diagnosed postoperative DVT. Caprini risk assessment model was used to detect high risk patients. No patients received any prophylaxis of VTE before surgery. Further data was analyzed for identifying the incidence of postoperative VTE. The t-test, χ² test or Wilcoxon rank-sum test was used to analyze the quantitative data and classification data, respectively. Results: Totally 345 patients who undergoing major thoracic surgery were enrolled in this study including 145 benign diseases and 200 malignant diseases.There were 207 male and 138 female, aging from 15 to 85 years. Surgery procedures included 285 lung surgeries, 27 esophagectomies, 22 mediastinal surgeries and 11 other procedures. The overall incidence of VTE was 13.9% (48 of 345) after major thoracic surgery including 39 patients with newly diagnosed DVT (81.2%), 1 patient with PE (2.1%) and 8 patients with DVT+ PE (16.7%). The median time of VTE detected was 4.5 days postoperative. There were 89.6% (43/48) VTE cases diagnosed in 1 week. The incidence of VTE was 9.0% in patients with benign diseases, while 17.5% in malignant diseases (χ²=5.112, P<0.05). The incidence of VTE in patients with pulmonary diseases was 12.6%, among that, in patients with lung cancer and benign lung diseases was 16.4% and 7.5 % (χ²=4.946, P<0.05), respectively. Regarding to Caprini risk assessment model, the incidence of VTE in low risk patients, moderate risk patients (Caprini score 5 to 8 points)and high risk patients(≥9 points)were 0(0/77), 15.2%(33/217) and 29.4%(15/51), respectively(Z=-12.166, P<0.05). In patients with lung cancer, 98.2% of patients were moderate risk or high risk; only 3 cases scored low risk. The incidence of VTE in moderate risk and high risk patients was 13.4%(18/134) and 32.1%(9/28), respectively, while it was 0(0/3) in low risk patients. Conclusion s The overall incidence of VTE after major thoracic surgeries is 13.9%, and the incidence of VTE after lung cancer surgeries was 16.4%. Most of the VTE cases occurr within one week after the surgery. Caprini risk assessment model can identify high risk patients effectively.