Abstract: A Semi-Free Flight mode in civil air traffic control system is proposed in this paper to improve the capability of free flight mode and centralized management mode, and multi-aircraft cooperative route planning is designed in this mode. This paper introduces the working mode of Semi-Free Flight ATC system, and presents collaborative route planning method, which is the most important model in Semi-Free Flight ATC system. This collaborative route planning method can plan routes based on real-time dynamic grid and cooperative dynamic planning algorithm for each aircraft either in flight or about to fly in real time satisfying all safe constraints. The final numerical simulations verify the correctness and practicability of the Semi-Free Flight theory and collaborative route planning method. about to fly in real time and can satisfy all safe constraints. The final numerical simulations verify the correctness and practicability of the Semi-Free Flight theory and collaborative route planning method.