Coherent laser radar refers to a detection method that uses a laser with a coherent light source to detect the target emission,and uses laser heterodyne reception to obtain target information through post signal processing.In this paper,the echo signal of the coherent laser radar passes through the photodetector,and the output frequency is high,the repetitive frequency period is long,and the processing data is large.A down-conversion technique is proposed to reduce the frequency to zero frequency,and applying the CIC and the HB filter form multi-stage sampling rate conversion to achieve data filtering and extraction.Finally,experiments show that this method can effectively achieve high signal-to-noise ratio samping for ranging at lower date rates.