Abstract: Based on the research of three-tier network service model of WebGIS and the technology of multi-server, this paper proposes a new extend model that processing GIS customs web requirement applying multi-server technology.In the procedure of constructing this model, proposes some methods to balance the load among servers.Storing and indexing GIS spatial data in multi-scale in database, keeping client's AOI data area in client side to decrease the client's requirement and transforming the load dynamically among servers can make the server cluster provide web service stably and quickly for the GIS client.It is significance for the development of GIS to issue the geographic information data on the Internet.