Aiming at the flight of small and light UAVs in near-ground 3D complex environments, this paper proposes a new path planning algorithm based on the Interfered Fluid Dynamical System (IFDS). The IFDS path planning algorithm, inspired by the phenomenon of fluid flow avoiding rocks in nature, has the advantages of clear physical meaning, analytical expression, fast computation, and producing smooth and high-quality path. In this paper, by introducing the obstacle cone into the IFDS algorithm, the obstacle avoidance behavior is restricted to the region only blocked by obstacles, as a result, the unnecessary bending of the path in unblocked region has been avoided, and also realizes the precise control of the minimum distance between the path and the obstacle. In addition, an expected tangent vector is introduced, which directs the flow in the trap area (TA) toward the parallel or perpendicular direction of the overlapping obstacle intersection line, generating a path that extends to the outside of the trap region, thus avoiding the UAV from falling into the TA.