Most of the natural vibration signals are stationary and modulated by the interference light signal of the distributed optical fiber vibration sensing system. As one of the key parameters of event recognition，amplitude information cannot be accurately obtained by traditional signal analysis methods. This paper used the fractional Fourier transform ( FＲFT ) method to analyze the nonstationary vibration signal of Ф-OTDＲ. In the unified amplitude，time and frequency domain，the amplitude of nonstationary signal can be extracted more accurately than the conventional method. Based on analyzing the causes of the non-stationary signal of Ф-OTDＲ，the applicable conditions of FＲFT are further discussed. The effectiveness of extracting the amplitude of Ф-OTDＲ signal by FＲFT is validated by the actual third-party damage of urban electric pipe gallery. In the continuous amplitude，time and frequency domain analysis，the fractional Fourier transform can extract the amplitude information of non-stationary vibration signal more accurately，which is helpful to improve the accuracy Ф-OTDＲ event detection and type analysis.