In order to increase the aircraft's survival in the flight mission, it is necessary to carry out flight mission planning, which includes TF/TA2(terrain following/terrain avoidance/threat avoidance). An approach to 3D-route planning based on A heuristic search algorithm was selected to determine the routes of fiber optic guidance missile's cruise segment. The cost function was discussed, which was mainly related to the physical obstacle, threat exposure, and aircraft performance characteristics. The digital map techniques were presented, which included setting “no-go” area according to fiber's safety requirement. The optimal or the sub-optimal route was obtained, while the cost function constraints were satisfied and the stored terrain obtained from a real terrain was digitized. The algorithm is validated through simulation and can fulfill the route planning task which focuses on the cruise segment of fiber optic guidance missile. In order to increase the aircraft's survival in the flight mission, it is necessary to carry out flight mission planning, which includes TF / TA2 (terrain following / terrain avoidance / threat avoidance). An approach to 3D-route planning based on A heuristic search algorithm was selected to determine the routes of fiber optic guidance missile's cruise segment. The cost function was discussed, which was mainly related to the physical obstacle, threat exposure, and aircraft performance characteristics. -go "area according to fiber's safety requirement. The optimal or the sub-optimal route was obtained, while the cost function constraints were satisfied and the stored terrain obtained from a real terrain was digitized. The algorithm is validated through simulation and can fulfill the route planning task which focuses on the cruise segment of fiber optic guidance missile.