Abstract: Objective：To retrospectively analyze the magnetic resonance imaging (MRI) signal differences between prostate cancer, benign prostatic hyperplasia, and normal prostate, and to explore the value of apparent diffusion coefficient (ADC) in prostate cancer grading. Methods：Forty cases of prostate cancer and eleven cases of benign prostatic hyperplasia in Zhongshan Hospital Affiliated to Fudan University between January 2013 to March 2014 were enrolled, which were all confirmed by surgery or biopsy. At the same time, 20 normal cases were arranged as the control group, which were healthy volunteers. All the patients and volunteers were obtained informed consent. The T2WI signal intensity, T1WI signal intensity (including unenhanced, arterial and venous phase) and ADC value of the three groups were compared after MRI and magnetic resonance diffusion weighted imaging (DWI). Then the correlation between ADC value of prostate cancer and Gleason score was analyzed to determine the critical value of ADC in the identification of high-risk and low-risk prostate cancer. Results：In terms of T2WI signal intensity and ADC values, there were significant differences among the three groups (P<0.05). In terms of T1WI signal intensity, only the difference of dynamic and venous phase in central gland of normal prostate was significantly different from that in prostate cancer and benign prostatic hyperplasia (P<0.05)，with the former higher than the latter two. The ADC value of prostate cancer was negatively correlated with Gleason score (r=-0.401, P=0.010). The higher the Gleason score, the smaller the ADC value. When the critical value of ADC was 0.70×10-3 mm2/s, the sensitivity of identifying low/intermediate-risk group and high-risk group for prostate cancer was 96.4%, and the specificity was 58.3%. Conclusions： T2WI signal intensity and ADC value can be used to identify prostate cancer, benign prostatic hyperplasia, and normal prostate. T2WI signal differences of dynamic and venous phase also have a certain reference value. The ADC value of prostate cancer is related to Gleason score, suggesting that it may be used for grading the clinical risk of prostate cancer.