As an important tool of space-based remote sensing system, space-borne laser altimeter has a lot of advantages, such as high accuracy, high resolution and ability of vertical resolution. So it has unique advantages and bright prospect in topographic mapping, deep-space exploration, global alert and monitoring and so on. The development of space-borne laser altimetry is briefly introduced, and the working principles of space-borne laser altimeter and push-broom laser altimeter using multiple beams are given respectively. For the latter, key technologies are analyzed, such as the transmission technology of multiple laser beams, the laser technology, the array detecting and receiving technology of multiplexing signals and so on. The application of space-borne laser altimetry is also described. Finally, the prospect of space-borne push-broom laser altimetry based on multiple beams is predicted and the development of space-borne laser altimetry in china is presented.