Abstract: In short-range monitoring of tall buildings, the phenomenon of pitch angle ambiguity always appears in the process of 3D terrain matching of ground-based synthetic aperture radar (GB-SAR) based on grid projection, which affects the interpretation of projection results. To mitigate these issues, in this paper, we propose a method designed to deal with the phenomenon of pitch angle ambiguity. Firstly, the transformation relationship between the image range-azimuth coordinate system and the north-east-up coordinate system under any GB-SAR observation geometry is derived. Furthermore, we realize the 3D terrain matching of GB-SAR based on the method of grid projection. Then, we analyze the causes of the phenomenon of pitch angle ambiguity. In addition, by judging whether there is effective laser point cloud data in each grid of 3D terrain grid matrix, the false image in the projection result is eliminated and the phenomenon of pitch angle ambiguity is corrected. The experiment results indicate that the false images in the projection results are effectively removed and the proposed method has a good performance in processing the phenomenon of pitch angle ambiguity.