Aiming at the problems of strong randomness of sampling point expansion and unsmooth path in the path planning process of RRT (Rapid-exploration Random Tree) algorithm,a constrained random sampling based RRT algorithm-CRS-RRT (Constrained Random Sampling-based RRT) is proposed.In this method,the potential energy function of gravitational field in artificial potential field method is introduced to constrain random sampling points to sample near the target point,so as to guide the random tree to grow towards the target point and improve the planning speed of the algorithm.Combined with the strategy of removing redundant nodes and Minimum Snap track smoothing method,a safe and smooth track that meets the dynamic constraints of UAV can be quickly generated in a complex three-dimensional environment. The simulation results show that the algorithm can effectively improve the speed of trajectory planning and shorten the trajectory length.