Abstract: Fat research of thigh is very valuable in the diagnosis of metabolic syndrome and metabolic dysfunction.However,it is more difficult to segment the subcutaneous fat and intermuscular fat in MRI images because of connected regions.The result of expectation maximization algorithm is used to improve level-set algorithm and realize automatic MRI image segmentation.Results show that the subcutaneous fat tissue,intermuscular fat tissue,and other tissues of thigh can be successfully segmented with the method.