Objective: To investigate and analyze the risk factors of massive hemorrhage in patients with renal cell carcinoma and venous tumor thrombus undergoing radical nephrectomy and removal of venous tumor thrombus. Methods: From January 2014 to June 2020, 241 patients with renal cancer and tumor thrombus in a single center of urology at Peking University Third Hospital were retrospectively analyzed. All patients underwent radical nephrectomy and removal of venous tumor thrombus. The relevant preoperative indicators, intraoperative conditions, and postoperative data were statistically analyzed by using statistical software of SPSS 18.0. The main end point of the study was intraoperative bleeding volume greater than 2 000 mL. Logistic regression analysis was used to determine the relevant influencing factors. First, single factor Logistic regression was used for preliminary screening of influencing factors, and variables with single factor Logistic regression analysis P < 0.05 were included in multivariate Logistic regression. In all statistical analyses, P < 0.05 is considered statistically significant. Results: Among the 241 patients included, there were 60 cases of massive hemorrhage, 48 males and 12 females, with a median age of 62 years. The number of non-massive hemorrhage was 181. There were 136 males and 45 females, with a median age of 59 years. Univariate analysis showed that the clinical symptoms (both systemic and local symptoms, OR 2.794, 95%CI 1.087-7.181, P=0.033), surgical approach (open surgery, OR 9.365, 95%CI 4.447-19.72, P < 0.001), Mayo grade (Mayo 3-4, OR 5.257, 95%CI 2.806-10.886, P < 0.001), American Society of Anesthesiologists (ASA) score (ASA level 3, OR 2.842, 95%CI 1.338-6.036, P=0.007), preoperative hemoglobin (OR 0.978, 95%CI 0.965-0.991, P=0.001), preoperative platelet count (OR 0.996, 95%CI 0.992-1.000, P=0.037), maximum tumor thrombus width (OR 1.061, 95%CI 1.033-1.091, P < 0.001), Complicated with bland thrombus (OR 4.493, 95%CI 2.264-8.915, P < 0.001), adrenalectomy (OR 3.101, 95%CI 1.614-5.958, P=0.001), segmental resection of the inferior vena cava (OR 2.857, 95%CI 1.395-5.852, P=0.004). There was a statistically significant difference in these aspects(P < 0.05). Multivariate Logistic regression analysis showed that there was a statistically significant difference in surgical approach (open surgery, OR 6.730, 95%CI 2.947-15.368;P < 0.001), Mayo grade (Mayo 3-4, OR 2.294, 95%CI 1.064-4.948, P=0.034), Complicated with bland thrombus (OR 3.236, 95%CI 1.492-7.020, P=0.003). Conclusion: Combining the results of univariate and multivariate Logistic regression analysis, the surgical approach, Mayo grade, and tumor thrombus combined with conventional thrombus were associated risk factors for massive hemorrhage during surgery for renal cell carcinoma with tumor thrombus. Patients who undergo open surgery, high Mayo grade, and tumor thrombus combined with conventional thrombus are at a relatively higher risk of massive hemorrhage.