After further study of traditional histogram equalization method, an improved algorithm of histogram equalization based on triangle function was put forward. This method is helpful to improve the contrast of image and makes image meet the requirement of image identification. Selecting the optimal parameters is the key to image enhancement technology, so a kind of easy way to choose the optimum parameters was selected. Image similarity was applied for image enhancement. The experimental results showed that the proposed method can enhance the image more effectively than the existing methods.