A high accuracy phase-shift ranging method is introduced.Carrier wave is realized by 1.08 GHz intensity modulation beat frequency signal produced by a dual frequency He-Ne laser and a polarizer,and it overcomes the modulation bandwidth limitation of the semiconductor laser for improving the accuracy of ranging.In order to reduce the difficulty of high speed ADC implement,undersampling method was used to collect waveform data according to the band-pass sampling theory and the theoretical basis was analyzed.The phase-shift of the sampled data was discriminated by all phase spectrum analysis method and the interception problem of phase discrimination data was strictly analyzed.In the system experiment,the accuracy of ranging could be about 0.1 mm when sampling rate was 50 MSa/s and the number of undersampling data was 157.Experiment results show that high accuracy ranging can be realized with the sampling rate far lower than measuring tape frequency when the undersampling all phase spectrum analysis method is used.