The issue of unmanned combat air vehicles (UCAV) to attack ground targets with laser guidance missile was studied. Considering the multiple constraints and high real-time requirement in air-to-ground weapon delivery trajectory planningwe proposed a general framework of autonomous attack trajectory planning systemestablished the Acceptable Launching Area (LAR) model for the missileand proposed a strategy to generate 3D weapon delivery trajectories based on an improved A-star algorithm. This algorithm combined the optimal constraints and UCAV motion constraints to find the appropriate successor nodewhich can greatly decrease the complexity of the algorithm. We chose an appropriate step to eliminate height change within each stepwhich helped to separate horizontal plane and the vertical plane of the trajectoryand then revised the vertical trajectory height based on normal acceleration. Simulation results prove that this strategy can quickly generate a 3D weapon delivery trajectory which can lead the vehicle to the target LAR and satisfy the constraints for launching a missile.