Objective：To investigate the pathological characteristics of patients with non - alcoholic fatty liver disease（NAFLD），their correlation with the magnetic resonance imaging estimated proton density fat fraction（MRI - PDFF）and liver function，and to explore the diagnostic value of MRI -PDFF in NAFLD. Methods：A total of 67 patients with NAFLD at the Department of Infectious Diseases，Affiliated Hospital of Nanjing University of Traditional Chinese Medicine were recruited from June 1，2021 to August 30，2023. Clinical characteristics were retrospectively analyzed based on different pathological fat content and non - alcoholic fatty liver disease activity score（NAS）. Correlations among pathological fat content，NAS，MRI - PDFF，body mass index（BMI），alanine aminotransferase（ALT），and aspartate aminotransferase（AST）were examined. A total of 33 individuals without hepatic steatosis confirmed by liver pathology were included as controls. The diagnostic value of MRI - PDFF for NAFLD was analyzed by receiver operating characteristic（ROC）curve. Results：Age，BMI，ALT，AST，MRI - PDFF，and NAS scores showed significant differences among different levels of pathological fat content. Similarly，BMI，ALT，AST，and MRI - PDFF differed significantly among differentNAS scores. Liver MRI-PDFF was significantly related to pathological fat content（r=0.775，P<0.001），and moderately related to NAS（r=0.478，P<0.001）and BMI（r=0.402，P=0.001）. Compared with the control group，the area under the curve（AUC）of MRI-PDFF for diagnosing NAFLD was 0.989，with a sensitivity of 0.94，specificity of 0.97，and an optimal cutoff value of 4.42%. Conclusion：MRI-PDFF is a quantitative measurement that can accurately reflect liver fat content，suitable for dynamic assessment and therapeutic monitoring of hepatic steatosis.