Aiming at the distributed sensing system based on multimode fiber is affected by the Brillouin scattering characteristics of multimode fiber, this paper uses finite element simulation to obtain the electric field distributions of six typical transmission modes of multimode fiber, and the Brillouin scattering characteristics of multimode fiber under single mode and mode superposition are simulated and studied from four aspects: Brillouin frequency shift, linewidth, max gain and Brillouin scattering spectrum. The simulation results show that the linewidth and max gain of different transmission modes of multimode fiber decrease slightly with the increase of the mode order, while the Brillouin frequency shift decreases significantly with the decrease of the mode order. Unaffected by strain and temperature, the Brillouin scattering spectrum after mode superposition is broadened compared to the single mode linewidth, and the max gain is greatly reduced.