Abstract: A novel hierarchical mobile IP network analysis model is firstly constructed in this paper. And then a scheme is proposed to set hierarchical mobile IP optimal size of regional network. After mathematical relations between handoff latency and the regional size of hierarchical mobile IP are studied, the conclusion can be drawn that there exists optimal size of regional network. Moreover, a minimum iterative function is adopted to deduce optimal MAP regional radius when handoff latency is minimum. Research results will be benefit to hierarchical mobile IP network planning and optimization.