In view of disadvantages of poor interactive, slow response and low scalability in traditional WebGIS application. This paper analyses the problem existed in WebGIS and then introduces the Rich Internet Applications. Discussed RIA approaches, in addition its advantages. Analyzed the construction mechanism of WebGIS development based on AJAX and Flex and gave implementation. The author believe that with more research on WebGIS based on RIA, RIA will play greater role in publishing geospatial information, furthermore. The geospatial information web sharing will become easier.