It is difficult to achieve high measurement accuracy and wide measurement rang i n phase ranging technology simultaneously.To solve this problem,this paper propose an interference demodulation phase ranging system.The theory of interference demodulation phase ranging system is derived and verified by experiment.The interference demo dulation phase ranging system uses polarization interference demodulation instead of traditional analog phase system.The analog phase circuit is simplified, and the additional phase shift noise is reduced.To solve the problem of a mbiguous range,this system uses frequency modulation continuous wave method.The ranging accuracy of interferenc e demodulation phase ranging system can reach 10－5.