The invention provides an SAR image synthesis method for enhancing target characteristics. According to the method, an SAR image and an optical image are effectively utilized for conducting synthesis, and therefore the target characteristics are enhanced. According to the technical scheme, the method comprises the steps of firstly obtaining the optical image and the SAR image shot from the same scene, conducting color preprocessing on the optical image through a color conversion module in a computer, utilizing a constant false-alarm for detecting high bright spots in the SAR image, conducting region merging on the bright spots, then, utilizing target prior information and the characteristics for completing detection post-processing, removing the false alarm, dividing the SAR image into a target region and a background region, utilizing the SAR image target position information by an optical image target characteristic extracting module for extracting a target region and the target characteristics of the optical image, finally, conducting three-channel color image synthesis on the SAR image and the optical image through an image synthesis module, and overlaying the extracted target edge of the optical image to the synthesis image for generating a final synthesis image.