Route planning is an essential component of pedestrian evacuation simulation. To enhance the performance of multi-scale simulation, we describe a new simple and efficient algorithm called Global A* which can outperform normal A* algorithm because it is not executed with each pedestrian. This algorithm is to do path planning for all the cells on the map before simulation. It is suitable for scenarios that have static exits such as canteens, cinemas and subway stations. Simulation experiments are carried out based on this algorithm and the social force model. Results demonstrate that with a certain size of map, Global A* shows a better performance when the population of pedestrians is larger than a threshold, which is 2000 when the map is 200*50.