Radar systems are used by air defense forces to detect and track aircraft. Route planning attempts to enhance safety by minimizing the exposure of the aircraft to the threat air defense systems while achieving the mission objectives. Based on Voronoi diagram theory, a flight route optimization method is introduced to insure the armed helicopter to penetrate the emery’s radar defense system at the lowest danger. The factors, such as radar cross section and distance between helicopter and radar, that affect the radar detection are firstly analyzed. Then Voronoi diagram and its application for route planning to minimize the detection probability of an armed helicopter are described introduced in details. Dijkstra algorithm is employed to solve the optimization problem and to obtain the initial flight path. The simulation of artificial potential field dynamic is performed to transform the initial path to the smooth flight route. Example analysis of a hypothesis armed helicopter shows that the developed method is helpful for the on-the-spot planning that combines aircraft flight performance and intelligence information regarding the estimated enemy weapon locations to develop routes that avoid or mask the enemy sensor and weapon envelopes.