Aimed at air route planning problems in complex environment, a route planning optimization method without threat based on the fundamental ant colony algorithm is proposed. The use of this method enhances the descriptive ability of the real flight circumstance to improve the effectiveness of route planning by reconstructing the route planning target function and comprehensively analyzing the information of terrain and threat in aircraft flight environment, including the factors such as route distance, time, fuel, cost and threat evasion ,etc. Still, the use of this method can save algorithm time and enhance efficiency of optimization by improving distance heuristic factor to introduce heuristic direction. The simulation results show that the use of this improved ant colony algorithm can save 10% of the optimization time and reduce 10odd iterative times compared with that of the fundamental ant colony algorithm.