Obejective: To investigate the value of multimodal magnetic resonance imaging (MRI) combined with prostate health index (PHI) in the differential diagnosis of Gleason grade of prostate cancer (PCa). Methods: A total of 150 patients with PCa confirmed by surgery or biopsy in our hospital from May 2020 to January 2023 were selected as the research objects. According to the pathological results of the patients and referring to the 2019 International Society of Urology (ISUP) PCa grading consensus meeting, the included cases were divided into 81 cases of low-grade PCa group ( Gleason score≤ 3+4 ) and 69 cases of high-grade PCa group (Gleason score≥ 4+3). Another 80 patients with benign prostatic hyperplasia confirmed by pathology during the same period were selected as the control group. All patients underwent multimodal MRI, prostate specific antigen (PSA) and other examinations, and the prostate health index (PHI) was calculated. Spearman rank correlation was used to analyze the correlation between multimodal MRI parameters and PHI levels with Gleason grade in PCa patients. ROC curve was used to analyze the diagnostic efficacy of multimodal MRI parameters and PHI level in differentiating Gleason grade of PCa patients. Results: The ADC value and Tmax of the control group, the low-grade PCa group and the high-grade PCa group gradually decreased, while the SImax and Rmax gradually increased, and the differences were statistically significant (P<0.05). The PHI level of the control group, the low-grade PCa group and the high-grade PCa group gradually increased, and the difference was statistically significant (P<0.05). The ADC value and Tmax of multimodal MRI parameters were negatively correlated with Gleason grade in PCa patients (r=0.536, 0.540, all P<0.001). The multimodal MRI parameters SImax and Rmax were positively correlated with Gleason grade in PCa patients (r=0.495, 0.507, all P<0.001). PHI level was positively correlated with Gleason grade in PCa patients (r=0.514, P<0.001). The Gleason grade of PCa patients was used as the state variable, and the combination of multimodal MRI parameters and PHI level was used as the test variable to analyze the ROC curve. The results showed that the AUC of multimodal MRI parameters (ADC value, Tmax, SImax, Rmax) and PHI levels in the differential diagnosis of low-grade PCa group and high-grade PCa group was 0.875 (95%CI: 0.775-0.976, P<0.001).The sensitivity and specificity were 81.0% and 83.7%, respectively, which were better than the single application of multimodal MRI parameters or PHI levels. Conclusion: Multimodal MRI parameters combined with PHI level can be used as an important diagnostic basis for distinguishing low-grade and high-grade PCa, and has certain reference value in the clinical application of preoperative Gleason grading. [ABSTRACT FROM AUTHOR]