Abstract: GBCSAR has the advantages of large field of view， high resolution， and three-dimensional resolution capabilities. It is of great significance in the field of complex scene deformation monitoring. However， there are a large number of target points in a large scene， and the traditional three-dimensional imaging method takes a long time， which is difficult to meet the demand for continuous monitoring. Therefore， this paper proposes a terrain surface imaging algorithm for GBCSAR. In scene deformation monitoring， terrain surface deformation can often reflect the trend of scene deformation. Aiming at this characteristic， the method in this paper will use the terrain surface to achieve imaging. The effective point surface obtained by the terrain surface extraction is used to replace the three-dimensional space target point of the scene， which realizes the dimensionality reduction imaging and improves the imaging efficiency. First， the geometric model and signal model of GBCSAR are given. Then it discusses the extraction method of the three-dimensional surface of the terrain， and then discusses the principle of the three-dimensional surface imaging algorithm. Finally， the feasibility of the method is verified through simulation experiments， and the imaging efficiency is compared with traditional three-dimensional imaging methods.