An important issue in the design of a mobile computing system is how to manage the real-time locations of mobile clients. In the existing commercial cellular mobile computing systems, a two-tier architecture is used. However, the two-tier architecture is not scalable and is not suitable to the new mobile computing applications in which there are a very large of mobile users. In the literatures, a hierarchical database structure is proposed. The location databases of different cells are organized into a tree structure to facilitate the search of mobile clients. Although this architecture can distribute the update and searching workload amongst the location databases in the system, it has the problem of heavy location update overhead and long search delay. This paper studies how to generate location update based on the distance-based update method in the tree structure. A location update generation method is proposed to calculate the optimal distance threshold with the objective to minimize the total location management cost.