Abstract: Three-dimensionalenvironmental modeling process is a fundamental problem in unmanned aerial vehicle (UAV) path planning.The use of traditional grid methods results in an exponential increase in the number of grids, which cannot guarantee a real-time process and effectiveness in high-precision 3D envi ronmental modeling. Considering the above problem, we a propose a 3D environmental modeling method with a high degree of dimensionality reduction. First, we use a traditional grid method to divide the 3D space. Secondly, we create a plane that contains the start point of UAV and the end of the target. Comparing the height of the plane with that of the obstacles, the obstacles below the plane can be ignored. We use the traditional grid methodto split the plane, which is used for planning the UAV trajectory to reduce the dimensionality of the environmental model. Finally, in a simulation experiment, we use A^* algorithm as the path planning method in a 3D environment of height reduction with high dimensionality reduction.By comparing the proposed method with the traditional grid method, it is concluded that the 3D environmental modeling method with a high dimensionality reduction does not only satisfy the demand of precision in environmental models but also improves the processing efficiency of the planning algorithm.