With fixed periods forest resources inventories and wide application of remote sensing,GPS technologies in forestry, large amount of spatial forest data have been collected in various forest resources bureaus. It is an urgent task to fully use these valuable spatial data to serve the national economic development and ecological construction. The expensive commercial geospatial software constrained small and middle-size companies to publish their spatial forest data. Fast development of open source software in the last decades provides an alternative solution to the commercial software. In the paper we developed a WebGIS based spatial forest information sharing system on county level with open source software FireFox, Apache Http Server, UMN MapServer and PostGIS/PostgreSQL. The system adopted four-tier architecture: client, Web server, application server and database server. The users can render the overlay information of spatial forest data layers, execute zooming in, zooming out, panning, and information querying functions. The system can provide most functions that commercial WebGIS has. It is suitable for small and middle-size companies which have limited budgets for developing WebGIS based spatial information sharing system to publish and share spatial information.