Thumbnail can greatly increase the efficiency of browsing pictures,videos and other image resources and improve the user experience prominently. Map service is a kind of graphic resource coupling spatial information and representation scale,its crafting,retrieval and management will not function well without the support of thumbnail. Sophisticated designed thumbnails bring users vivid first impressions and help users make efficient exploration. On the contrast,coarse thumbnail cause negative emotion and discourage users to explore the map service positively. Inspired by video summarization,key position and key scale of web map service were proposed. Meanwhile,corresponding quantitative measures and an automatic algorithm were drawn up and implemented. With the help of this algorithm,poor visual quality,lack of map information and low automation of current thumbnails was solved successfully. Information entropy was used to determine areas richer in content and tran-scale similarity was calculated to judge at which scale the appearance of the map service has changed drastically,and finally a series of static pictures were extracted which can represent the content of the map service. Experimental results show that this method produced medium-sized,content-rich and well-representative thumbnails which effectively reflect the content and appearance of map service.