To explore the value of magnetic resonance (MR) diffusion tensor imaging (DTI) in the differential diagnosis of dermatomyositis and muscular dystrophy. Methods: A total of 42 patients with pathologically confirmed dermatomyositis and 23 patients with muscular dystrophy were included. All patients underwent routine MR and DTI imaging of both thighs, comparing the signal intensity (SI), apparent diffusion coefficient (ADC), and fractional anisotropy (FA) of the thigh muscle groups between patients with dermatomyositis and muscular dystrophy. Independent samples t-test and receiver operating characteristic curve (ROC) analysis were used for all parameters. Results: There was a significant difference in ADC and FA values of the thigh muscle groups between patients with dermatomyositis and muscular dystrophy (P<0.01, P< 0.05), while there was no significant difference in SI (P>0.05). Among them, the DTI parameter ADC had a high diagnostic value in differentiating dermatomyositis and muscular dystrophy, with an area under the curve (AUC), sensitivity, and specificity of 0.723, 54.1% , and 78.1% , respectively. Conclusion: The functional sequence DTI, as a supplementary technique to conventional MR, helps to distinguish between dermatomyositis and muscular dystrophy.