An algorithm for the digital elevation model (DEM) interpolation in the spiral scanning airborne lidar system is proposed. First, the scanning characteristics of this spiral scanning lidar system is described and the principle of real-time calculation of the overlapping area is clarified. Then the improved method of triangulation iterative encryption filtering is introduced and is also used to separate the terrestrial and non-ground points. Finally, the DEM interpretation is carried out based on the random forest. The experimental results show that with this method, the DEM interpolation in the spiral scanning airborne lidar system can be realized with an interpolation accuracy meeting the data requirements for industrial production.