A “man-in-the-loop” task planning strategy was proposed to satisfy the growing autonomous need for Unmanned Combat Aircraft Vehicles (UCAVs).A fast trajectory planning scheme was put forward based on Gauss Pseudospectral Method (GPM) considering the requirement of UCAVs.In the scheme the UCAV aerodynamic characteristics the thrust characteristics and the influence of atmosphere environments were taken into consideration based on which a UCAV model with high accuracy was built up.A trajectory planning model was built up based on optimal control theory and analysis to various complicate constraints such as the UCAV flight envelop in real environment and three dimensional obstacle battlefields.Finally the basic principle of using GPM to solve the optimal control problem for UCAV trajectory planning was analyzed.Simulation results show that GPM can generate a continuous viable and optimal trajectory satisfying various complicated constraints.