A phase sensitive optical time domain reflection system demodulation method based on clock homologous I/Q demodulation is proposed. The influence of the non-homologous disagreement between the modulation signal and the mixing signal on the demodulation results is analyzed. The method using clock homologous modulation signal of the acoustic optical modulator, the chopper signal and the I/Q mixing signal is adopted to eliminate the influence of the residual frequency. Double piezoelectric ceramic is used as the disturbance source, and the amplitude and phase of the backward Rayleigh scattering light can be obtained in real time by I/Q demodulation, so as to achieve the location and reduction of the disturbance. The experimental results show that the system can detect the sinusoidal disturbances at 5 km and 9 km effectively, and the signal to noise ratio of the positioning signal is up to 17.8 dB and 16 dB, respectively. The phase demodulation results accurately restore the sinusoidal disturbance, and the fitting coefficients of the sinusoidal curves are 0.994 and 0.991 respectively, and the root mean square error is 0.116 and 0.141, respectively. Furthermore, the experiment verifies that the method can measure the phase sine curve under different disturbance amplitudes. The different disturbance frequencies can be obtained accurately, and the phase change amplitude at disturbance location has a good linear relationship with the disturbance intensity. The linear fitting coefficient is 0.992, and the root mean square error is 0.499, both are better than the non-homologous demodulation result.