For using route planning on embedded system of small fixed-wing UAV, design an automatic route planning method based on sparse A* algorithm. According to the application environment, characteristics and motion constraints of small fixed-wing UAV, establish the environmental model and the motion model of route planning. Use unit decomposition method to realize environmental model of fight area and the motion model of UAV. Use sparse A* algorithm for route planning, and give the operation program. Two different heuristic functions were simulated and analyzed. The results show that the safety of route planning is improved and the algorithm is optimized.