Objective To investigate the clinical staging and prognosis evaluation of bladder urothelial carcinoma by multimodal MRI. Methods A total of 81 patients with bladder urothelial carcinoma from November 2017 to January 2021 in our hospital were selected as the research subjects, and all underwent multimodal MRI examination. All patients fasted for 4-6 hours before the examination, and urinated for 60 minutes before the examination until the completion of the examination. Supine bladder MRI was performed with a 1.5T whole-body superconducting scanner. The scanning range was from the bifurcation of the abdominal aorta lower border pubic symphysis. All patients underwent tumor resection within 1 week after multimodal MRI examination. Results The sensitivity and specificity of multimodal MRI for T3 and T4 were higher than conventional MRI, and the difference was statistically significant (P<0.05). There was no significant difference between multimodal MRI and conventional MRI in sensitivity and specificity of T1 and T2 (P>0.05). Multimodal MRI in the TI stage showed nodular abnormal signal shadow on the left bladder wall, with equal signal on T1WI, slightly low signal on T2WI, high signal on DWI, and local ADC value decreased slightly. The muscle layer was not involved; no obvious recurrence was found in the follow-up one year after treatment, and the prognosis was good. T2-stage multimodal MRI showed nodular abnormal signal shadow on the right side of the bladder, with equal signal T1WI, slightly low signal T2WI, high signal DWI, decreased ADC value. The demarcation between the part and the muscle layer was unclear; no obvious recurrence was found in the re-examination two years after treatment, and the prognosis was good. Multimodal MRI in T3 stage showed that the left parietal wall of the bladder showed a mass abnormal signal shadow, with equal signal T1WI, slightly low signal T2WI, high signal on DWI, decreased ADC value. After enhanced scanning, the lesion was significantly enhanced, and the mass corresponds to the muscle layer. The structural display was interrupted, with infiltration of the surrounding fat space; no obvious recurrence was found in the re-examination two years after treatment, and the prognosis was good. Multimodal MRI in T4 stage showed irregular mass-like abnormal signal shadows in the right posterior wall of the bladder, isointensity on T1WI, isointensity on T2WI, hyperintensity on DWI, and decreased ADC value. After enhanced scanning, the lesions showed mild persistent enhancement and mass Breaks through the bladder, involving the uterus and rectum; prognosis improves. Conclusion Multimodal MRI can accurately judge the clinical staging of bladder urothelial carcinoma, more accurately evaluate the prognosis of patients.