This paper conducts a solid research work on 3D path planning problem for fixed-wing UAV, environmental construction and particle swarm optimization (PSO) with improvement strategies. In this path planning technique, the design variable denotes the 3D way-points of the fixed-wing UAV and objective function indicates the total cost of the UAV in a particular trajectory built by the way-points. The environment is constructed using a random mountain model, the constraints consist of the boundary of the map, the environment and dynamic constraints. The research models the variables and objective function, designs the improvement strategies, solves the way points and completes the path planning and uses different parameters setup to compare of the performance of path planning.