This paper proposed a method of path planning in three-dimensional space based on concentric spherical coordinate and improved particle swarm optimization algorithm. First the model of three-dimensional path planning of UAV was analyzed. Then the encoding method based on concentric spherical coordinate system was given. The constraints were combined with the improved particle swarm optimization algorithm to make the path more rational and the searching more efficiently. At the same time using Matlab7.0 as the development tool for simulation, the simulation analyses showed that the method of path planning in this paper is applicable and acceptable, which could achieve the goal of terrain following and threat avoidance (TF/TA2).