对相位解调相位敏感光时域反射仪(φ-OTDR)系统中干涉衰落问题进行了研究。同一频率多次脉冲扫描显示出相似的衰落波形，而不同光频有不同的衰落波形。通过改进现有瑞利散射随机性和相干性物理模型，推出了瑞利散射系数是激光频率和有效折射率的函数，合理解释了上述实验现象。为了消除干涉衰落导致的系统误报问题，提出了一种基于多频率综合判决的方法，有效地区分并排除了误报，提高了整个φ-OTDR系统相位解调的准确性。

The characteristics of interference fading in the phase-demodulated phase-sensitive optical time domain reflectometer(φ-OTDR) system are investigated. It is found that the fading waveforms have high similarity for different pulse scans, but obvious differences for different optical frequencies. An improved model for randomness and coherent noise of Rayleigh scattering is presented. It can be concluded that the composite Rayleigh scattering coefficient is a function of laser frequency and the index distribution, which could explain the experimental results reasonably. In order to eliminate the false alarms due to interference fading, a multi-frequency method is proposed, which can improve the accuracy of the phase demodulation in the φ-OTDR system.