The GIS technology provides a new mechanism and an effective method to develop Digital City, which is an important node of implementing the digital earth. In this paper, the framework of Digital City based on GIS is investigated. Through GIS service, the urban spatial data and attribute data can be accessed and integrated seamlessly to various Digital City applications. Moreover, a Digital City application is given to illustrate the key techniques based on MapObjects of ESRI and an objects-oriented developing tool, namely, Visual C++. Experiment results show the robustness and efficiency of the proposed method.