In order to avoid the nonlinear effect of the optical fiber and the insensitivity of the front-end vibration under the high power pulse, a new fiber sensing structure method of composite fiber was adopted, which was analyzed theoretically and verified experimentally. By using the hybrid of multi-mode fiber and single-mode fiber as the sensing fiber method, the distance data of the optical fiber sensing was obtained by processing the sensing signals under different power pulses. The results show that the new composite optical fiber sensor structure can detect the vibration signal of 30km. At the same time, the sensing function of multi-mode fiber in Raman system was further studied, and the sensing characteristics of multi-mode fiber were discussed. The new sensor structure provides an important reference for the scientific research and engineering application of the multimode fiber in the field of phase-sensitive optical time-domain sensing.