Objective. To assess the efficacy of three-dimensional conformal radiotherapy (3D-CRT) combined with GT chemotherapy (gemcitabine+docetaxel) in the treatment of advanced bladder cancer and its influence on inflammatory factors and immune function. Methods. A total of 42 elderly patients with advanced bladder cancer who were admitted to our hospital from January 2019 to January 2020 were included and assigned to the GT group (21 cases) receiving GT chemotherapy and combination group (21 cases) given 3D-CRT combined with GT chemotherapy. The clinical efficacy, immune function, inflammatory factors, tumor markers, urinary angiogenesis molecules before and after treatment, 1-year survival rate, 2-year survival rate, and incidence of adverse reactions of the two groups were compared. SPSS 22.0 statistical software was used for data processing and analysis. Results. The combination group had 5 cases of CR, 12 cases of PR, 3 cases of SD, and 1 case of PD, with an ORR of 80.95% (17/21), which was remarkably higher than the ORR of 57.14% (12/21) in the GT group which had 3 cases of CR, 9 cases of PR, 5 cases of SD, and 4 cases of PD ( P < 0.05 ). The 1-year survival rate of the combination group was 76.19% (16/21), and the 2-year survival rate was 47.62% (10/21), which were higher than the 1-year survival rate of 47.62% (10/21) and 2-year survival rate of 19.05% (4/21) in the GT group ( P < 0.05 ). The two groups presented similar results in terms of adverse reactions rate ( P > 0.05 ). After treatment, the combination group obtained significantly lower levels of urinary bladder cancer antigen (UBC), nuclear matrix protein-22 (NMP-22), vascular endothelial growth factor (VEGF), and basic fibroblast growth factor (bFGF) than the GT group ( P < 0.05 ). The CD3+, CD4+, and CD4+/CD8+ levels of the two groups of patients were lower than those before treatment ( P < 0.05 ), but no statistical difference was observed between the two groups after treatment ( P > 0.05 ). The levels of interleukin-6 (IL-6) and interferon-γ (IFN-γ) of the two groups witnessed a decline after treatment, with lower results in the combination group as compared to the control group ( P < 0.05 ). Before treatment, no significant difference in the Generic Quality of Life Inventory-74 (GQOLI-74) score between the two groups was found ( P > 0.05 ). After treatment, the combination group had higher GQOLI-74 scores than the GT group ( P < 0.05 ). Conclusion. 3D-CRT combined with GT chemotherapy yields a significant effect on the treatment of elderly advanced bladder cancer by effectively protecting immune function, mitigating inflammation, inhibiting tumor marker levels and the expression of angiogenic molecules, and improving patients’ survival.