The Infrared images have been applied in clinical diagnoses, but the images are noisy and blurred. Therefore the smooth processing that can keep edges is needed. Traditional smoothing methods have the common defect that they smooth not only the noise region but also the edges. AMSS (affine morphological scale space) algorithm can be used to better save the edge information, it has the Partial Differential Equation that is of morphological affine invariability and contrast invariability. The smooth processing method based on AMSS is introduced to handle the infrared image in this paper, and the better performance is obtained.