Spaceborne laser altimeter has the characteristics of large calibration site, large amounts of detectors, poor work conditions. To achieve the goal of precise timing, data collection and processing of ground-based calibration system, a software designing scheme is put forward, and the implementation algorithm of the software is introduced in detail. With expanding its peripheral equipment, the function of data processing and timing is mainly realized. At the same time, four modules of the systan are module of processing time tag data, calculating the centroid of laser footprint in the ground, correcting the atmospheric refraction delay, and timing. The data from “ZY3-02” satellite is processed in site experiments, and the results show that the design of the software is feasible.