The paper analyzes the problems existed in WebGIS that traditional WebGIS is independent and isolated and there is no sufficient interoperability among different systems. Then the paper discusses the application of XML on WebGIS in two aspects

namely the data interoperability and the function interoperability. After this

a schema for open WebGIS based on XML is proposed. Since the schema is designed with the open technologies

so it is different from the traditional one. The system devoloped according to the schema is interoperable

extensible and interactive. Finally based on the above schema

a prototype system is developed to test the theory correction and technique feasibility of the schema. With the prototype

some tests for the integration of the heterogeneous geospatial data are implemented and some satisfied results are achieved.