Objective: To evaluate the impact of deep invasive tumor thrombus on the surgical complexity and prognosis of patients with renal cell carcinoma complicated with inferior vena cava tumor thrombus. Methods: We retrospectively reviewed the clinical data of 94 patients with non-metastatic renal cell carcinoma complicated with inferior vena cava tumor thrombus, who underwent surgical treatment in Peking University Third Hospital from January 2017 to June 2020. The patient’s general condition, clinicopathological characteristics, surgery and survival information were collected. The patients were divided into two groups based on the intra-operative findings of tumor thrombus adhesion to the venous wall, of which 64 cases were in the deep invasive tumor thrombus (DITT) group and 30 cases were in the non-invasive tumor thrombus (NITT) group. Chi-square, t test and Mann-Whitney U test were used for categorical and continuous variables respectively. Kaplan-Meier plots and multivariable Cox regressions were performed to evaluate the influence of DITT on the prognosis of the patients with renal cell carcinoma with inferior vena cava tumor thrombus. Results: DITT significantly increase the difficulty of surgery for the patients with renal cell carcinoma with venous tumor thrombus, which was mainly reflected in the longer operation time (362.5 vs. 307.5 min, P=0.010), more surgical bleeding (1 200 vs. 450 mL, P=0.006), more surgical blood transfusion (800 vs. 0 mL, P=0.021), more plasma transfusion (200 vs. 0 mL, P=0.001), a higher proportion of open surgery (70.3% vs. 36.7%, P=0.002), a longer post-operative hospital stay (9.5 vs. 8 days, P=0.036), and a higher proportion of post-operative complications (46.9% vs. 13.8%, P=0.002). DITT was associated with worse overall survival of the patients with renal cell carcinoma with inferior vena cava tumor thrombus (P=0.022). Even in the multivariate analysis, DITT was still a poor prognostic factor for the overall survival of these patients [HR: 4.635 (1.017-21.116), P=0.047]. Conclusion: For patients with non-metastatic renal cell carcinoma with inferior vena cava tumor thrombus, DITT will significantly increase the difficulty of surgery, and may lead to poor prognosis.