The multi-frequency detection is an important way of interference fading suppression in the optical fiber sensing system of Φ-OTDR. But, there is the problem of complex structure caused by multi-frequency generation. A multi-frequency pulse generation method based on the optical fiber frequency-shifted delay loop is proposed in this article. Optical fiber loop structure is designed with frequency shift, amplification, delay, filtering, isolation and other functions. The generation and multiplexing of multi-frequency detection pulses are realized by using this simple structure. The data alignment and data aggregation of Rayleigh backward scattering beat signal are realized by using the pulse delay compensation algorithm and rotated-vector-sum algorithm, respectively. The experimental results show that the sensing system can optimize the fading probability from 26. 43% to 0. 93% with the 10. 33 km sensing fiber by the generation of multi-frequency detection pulses containing six frequency components, and achieve the accurate location of the vibration signal with a signal-to-noise ratio of 5. 29 dB and the linear demodulation of the vibration signal with a correlation coefficient of 0. 997. It provides a new solution of anti-fading demodulation of vibration signal for Φ-OTDR in complex environment.