In order to improve the efficiency of the quadrotor long-distance trajectory planning in 3D complex scene, this paper proposes a real-time quadrotor trajectory planning method based on local soft-constrained optimization. The method can be divided into the following two steps: Firstly, the safety distance constraint is added to theta* algorithm, and the heuristic function is improved by using the turning cost to reduce the time consumption caused by quadrotor turning, and finally the initial path composed of a small number of key points is generated; Secondly, the local optimization strategy is used to optimize the segments with potential safety hazards in the initial path based on soft constraints, and the Hodograph property of Bézier curve are used for time allocation to ensure the continuity, smoothness and dynamic feasibility of the trajectory and improve the flight efficiency of quadrotor. Experimental results show that the proposed method has shorter flight distance and flight time and higher planning efficiency while ensuring the safety of quadrotor. This method can also be successfully applied to the actual quadrotor flight.