The GIS Web service technology provides a new mechanism and an effective method to develop next generation GIS system. This paper investigates the method to develop Web GIS based ITS application systems with GIS Web service technology. Based on the OGC GIS Web service framework and SOA architecture, a distributed and Web service enabled Web-GIS based ITS application system is investigated. The GIS-T Web services are exposed and discovered in the GIS-T Web service portal. Through GIS-T Web service, the hosted spatial data and GIS functionalities can be accessed and integrated to the different customized ITS applications. The GIS content and capabilities can be integrated into the customized ITS application systems for sharing geographical information and data. ITS application systems can access GIS-T Web services through Web protocols such as HTTP and XML without concern for how each service is implemented. The GIS-T Web service is a promising architecture for implementation next generation GIS-T information systems. It has very good promotion prospect and important value for the system design and construction for various Web GIS based ITS application systems