X-ray technology is being increasingly employed for the clinical diagnosis and remedies in recent years. In order to distinguish small lesions in a medical X-ray image correctly, digital image processing technology is linked with clinical diagnosis. A method in medical image processing based on multiscale fractal feature (D_MF) was applied in this paper. The D_MF values of different regions in a medical image are normally different. According to the values of the D_MF, small lesions in a medical X-ray image can be detected. This method has been applied to a digital bone fracture X-ray image. Experimental result showed that the D_MF values of the background regions are between 0.005 and 0.020; the D_MF values of the normal regions are between 0.040 and 0.070; and the D_MF values of the knot regions are between 0.100 and 0.200. This method has stronger distinguishing ability, showing better performance in clinical diagnosis.