This paper discusses the problem of path planning for fixed-wing unmanned aerial vehicles (UAVs) in a complex static 3D environment. The main idea is to produce a smooth path that conforms to the safety corridor constraints and maneuverability of the fixed-wing UAV. The representation of a static 3D environment is created using the visibility graph method, where this method generates waypoints and all possible paths in the environment. After being given a starting point and a destination point, the Theta∗ algorithm works to calculate the shortest path on a 3D environment. The shortest path obtained is then smoothed using a Bézier curve-based smoothing path planning method that meets the proposed constraints. The results of this proposed method are compared with previous work by applying the relevant comparative criteria. The simulation results show that the proposed method is safer than the previous method with the smallest distance to the obstacle of 4.73 m.