In order to solve the defect of traditional single fractal dimension in signal representation, a multi-scale fractal dimension estimation method based on morphological calculation was proposed. The normal, misfire, and excessive valve clearance fault signals of diesel engine were analyzed and compared with a single fractal dimension method. The results show that the multi-scale fractal dimension based on morphological calculation can accurately classify the signals of diesel engine in different states, and the calculation is simple and fast, which has good fault diagnosis effect.