In space-borne laser altimeter system, the range between satellite and target was calculated by the weak received signal which was transmitted from laser device and reflected by earth surface, and the accurate location and elevation of laser footprint was acquired by combining satellite precise orbit with attitude data. The elevation error was mainly affected by the device noise, the environment and the target parameters, and there is no complete analyzing model of location and elevation error for spaceborne laser altimetry system. The error model of laser ranging for solid surface was simplified and improved. Meanwhile, the location and elevation error analysis model of laser footprint was established in this paper. Utilizing airborne lidar data with better spatial resolution and elevation accuracy, the elevation deviation of GLAS data were evaluated, and the result was consistent with the error model. It is proved that on the flat surface of ice sheets the elevation accuracy of GLAS system can meet its design value of approximate 15 cm. This research is instructive for elevation error assessment and system parameters designing of laser altimeter system.