Abstract: Abstract: Accurate acquisition of cavity ring-down Signal is the basis of quantitative detection of gas concentration by cavity ring-down spectroscopy. Aimed at the characteristics of cavity ring down signal, a cavity ring down signal acquisition and processing system based on FPGA is designed. Based on the FPGA hardware logic, the system realizes the high speed acquisition of the cavity ring down signal, the accumulation average of the corresponding point and the transmission of the USB data under the excitation of trigger signal. The completed system was tested in the cavity ring down system, the consistency of the data from the data processing system and the foreign data acquisition card reached 99.4%. The results show that the data acquisition and processing system can fully meet the acquisition requirements of cavity ring down signal.