The need for managing distributed systems and providing seamless service is prominent in E-Government. SOA can potentially address those needs and provide software architecture for the interaction of existing and new distributed systems in E-Government. Through analyzing the characteristics of SOA and Web Services, Web Services is considered as the most appropriate technology for implementing SOA. On this basis, the government service bus (GSB) is presented that is responsible for managing services and interaction in services. A software architecture of E-Government based on SOA is proposed, which addresses the complex of the integration and interaction and heterogeneous systems in E-Government system, and may extend into other areas such as E-Commerce, E-Healthcare areas.