A kind of infrared image threshold denoising and enhancement method based on discrete stationary wavelet transform and non-linear gain was given. After making discrete stationary wavelet transform to an infrared image, denoising was done by the method given in the high frequency subbands which was in the better resolution levels and enhancement was done by combining denoising method with non-linear gain method in the high frequency subbands which was in the worse resolution levels. According to the experimental result, the given algorithm can reduce the noise of infrared image effectively while it enhances the contrast of infrared image well. In visual quality, the algorithm is better than the traditional unshaped mask method and histogram equalization method.