摘要： The spacecraft landing on Mars or other planets generally requires measuring relative velocity and distance between itself and the land. The measurement demands high accuracy and high reliability. This paper presents an optical frequency stepped chirp modulated pulse train coherent lidar technology for range and velocity measurement. This paper advances an all-fiber structure lidar. It has advantages of small size, high efficiency, low power consumption and stable performance. This paper introduces the optical frequency stepped chirp modulation technology. It gives the semiconductor seed laser theoretical model of driver current versus laser frequency, and computes the modulation waveform. We use an AWG (arbitrary waveform generator) to load the waveform and get the optical stepped chirp modulated pulse train. This paper derives the ambiguous function of the lidar. This function provides a powerful tool to analyze the property and find the highlight property of this lidar: high effective time-bandwidth products. The property gives high range accuracy and velocity accuracy. The signal processing method is advanced. The algorithm can get the range and velocity simultaneously. The Doppler effect caused by target motion is analyzed. The rang walk error caused by Doppler effect is compensated by special algorithm.