Real-time mobile GIS applications, e.g. car navigation, need effective spatial data storage model fit for the mobile compute environment. Therefore, Physical Storage Format (PSF) is an important technical bottleneck of some real-time requirement such as map browsing, route planning, driver guidance, point of interesting (POI) search and 3D visualization. This paper proposes a new storage model based on mobile navigation application, named as Navigation Data Format (NDF). The NDF adopt multi-level model to organize spatial data (e.g. map of background) that has notable effect to reduce the memory cost of map browsing. The road network data of NDF is built based upon hierarchical topological structure which can support the speed-up way finding algorithm. The page frameworks of the NDF compared with current PSF, have introduced some new features. Firstly, NDF has good adaptability to various kinds of mobile computer environment. Secondly it provides facility for incremental update. Further, the NDF has been adopted as candidate national standard of China.