The distance between satellite and target is calculated through extracting parameters of received waveforms, combined with orbit and attitude information, the accurate location and elevation of laser footprint are acquired. For common Gaussian laser beam, the spatial distribution of energy decays rapidly with the increase of laser spot radius, which is not suitable for detecting the complicated and layered ground target, while the flattened Gaussian beam can overcome this drawback. According to the theory of flattened Gaussian beam and waveform model of laser altimeter, the primary parameters of received waveform are derived and verified using laser altimetry waveform simulator, waveform processing algorithm and actual geoscience laser altimeter system (GLAS) waveforms. The results show that the contrast deviations of different order laser pulses are all less than 3%, the waveform width and range error increase with the rising of target slope or order number, and the corresponding range error of the 4th order flattened Gaussian beam under target stope of 0.05 is more than 10 cm range error.