Abstract: A component-based WebGIS system Geo-Union is firstly introduced in the paper, and the architecture, the functional partition and the web application mode of Geo-Union are discussed. Then a spatial cache framework is designed and adopted in Geo-Union to improve its performance in network environment. There are three levels within the spatial cache framework: spatial database cache, network spatial cache and spatial data proxy server, and those caches play different roles in different situations to improve spatial data access performance of Geo-Union.