Based on the spatial distribution of laser beam intensity of laser altimeter and terrain characteristics mode, the simulation process of lidar waveforms and the function of each model of simulation program based on IDL were presented in detail. The modeled and actual lidar waveform pairs were compared using the Pearson correlation, and the correlation coefficients were always larger than 90%. The variation of the waveform with different parameters of the laser altimeter and the terrain was analyzed. The simulation is a direct and effective method to model the lidar echo from arbitrary terrain, which provides an important technical mean to analyze the lidar waveforms.