Abstract: The digital terrain model is an important aspect in mobile robot technology research. Based on the object-oriented method, this paper presents an object-oriented digital terrain model for the mobile robot navigation, and discusses the extended symbolic projections and the method of spatial reasoning for topological relations in this model. The digital terrain model introduced in this paper has been used in our terrain database and path planning system that has been developed. Mobile robots, digital terrain model ,object-oriented method, symbolic projections