A new method to enhance the contrast of infrared image was given, which was based on discrete stationary wavelet transform and non linear gain. After making discrete stationary wavelet transform to an infrared image, de noising is done in the high frequency sub bands with better resolution. Enhancement effect is obvious by combining de noising method with non linear gain method in the high frequency sub bands with worse resolution. A new criterion to evaluate quality of image was given. Experimental results show that the new method can reduce colored noise, additive gauss white noise and speckle noise in infrared image effectively while it also enhances the contrast of infrared image well.