An improved method was proposed to solve the problem that the heuristic value of D* Lite algorithm was not accurate and the planned path passed through the vertex of obstacle grid. A more accurate distance was used to replace Chebyshev distance as the heuristic value. For the new distance, the cost values of linear distance and oblique distance were distinguished. The extended nodes were classified and a safety factor was introduced for the dangerous nodes. Finally, the improved algorithm was simulated. The simulation results show that the improved D* Lite algorithm has less expansion times and better performance because of its more accurate heuristic value; when the safety factor is introduced, the dangerous node will not be considered as the first choice of the path, it solves the problem that the planned path passes through the vertex of obstacle grid obliquely.A very safe path can be planned in the pre-planning or re-planning stage.