Because of many advantages, Lidar based on synthetic aperture theory is becoming research hotspot and coming near practicality. Based on this background, an overview of synthetic aperture lidar is given. In this paper,the importance of developing a new type of lidar is briefly analyzed after introducing the advantages and defects of the traditional lidar. The principle and progress of synthetic aperture lidar are introduced and a typical synthetic aperture lidar system is described. Finally,the existed difficulties of developing synthetic aperture lidar are discussed and the application prospect is predicted based on the analysis of the domestic state of the art.