The efficiency of power line patrol is highly improved by Unmanned Aerial Vehicle, and it can be further improved if those collected digital images can be processed with computers. Image enhancement is an important procedure for image process. Two different kinds of gray image enhancement algorithm based on random mathematics model and fuzzy mathematics model respectively are discussed combined with the characteristics of power line gray image, and the performance of these algorithms is compared. The disadvantage of each current image enhancement algorithm in power line gray image is analyzed. Accordingly, we provide an improved image enhancement algorithm based on fuzzy mathematics model and its applicability is tested with examples.