On clinical applications, many magnetic resonance (MR) Images obtained directly by the instruments are not satisfied by doctors. For example, there are some noises and poor contrast in the MR images. These shortcomings would affect the efficiency of feature extraction or recognition later. To solve this problem, the paper proposes a synchronization algorithm of denoising and contrast enhancement. By constructing a differential equation of limited adaptive histogram equalization, the edge denoising and enhancement are completed with the improved PM model. The algorithm draws on the advantages of the two original models, and the practicality and accuracy are proved by the results of the experiments.