With the development of Internet technology, traditional WebGIS servers delay or even deny service when dealing with high concurrent access from large groups of users. After analyzing the problem, this paper proposes a framework of WebGIS servers based on cloud platform, which aims at dealing with high concurrent access. The framework uses cloud platform to provide flexible computing and storage resources for WebGIS servers, and alleviates bottleneck of high concurrency in three ways:load balancing, cache design, and database cluster. Open source server software GeoServer is selected to deploy as WebGIS application experiment. Experimental results show that usage of data cache can evidently reduce response time of WebGIS service. Compared with a single physical server, the WebGIS server clusters based on cloud platform can effectively process high-concurrence requests, and with the extending of cluster scale, the WebGIS system based on cloud platform can achieve good speedup.