Abstract: Purpose: To investigate the effects of two preparation methods on the image quality of bladder cancer magnetic resonance imaging (MRI) and the diagnostic performance of differentiation of muscular invasion of bladder cancer. Methods: 76 cases of bladder cancer patients underwent preoperative MRI. They were divided into two groups and underwent two different bladder preparation methods respectively. The image quality of the two methods on high-resolution T2WI combined with diffusion-weighted imaging (DWI) and dynamic contrast-enhanced imaging (DCE) was compared. To determine whether the MR images of the two groups of patients have any influence on the diagnostic performance of the bladder cancer lesions in muscle invasion. Results: The consistency between the two readers was good. Compared with group B (urinate 2 hours prior to bladder MRI with no drinking), group A (after 4 to 6 hours of fasting, inject about 100 ml of physiological saline into the bladder before the examination through the catheter) had a better bladder filling degree. In terms of diagnostic efficiency, the sensitivity and accuracy of group A in diagnosing muscle-invasive bladder cancer were higher than those of group B, the difference has no statistically significant. Conclusion: Injecting an appropriate volume of physiological saline into the bladder before MR examination can be used as a clinical assistant bladder preparation method which help patients with bladder cancer properly fill the bladder, improve the quality of magnetic resonance images, and help improve the diagnosis of bladder cancer with magnetic resonance.