Herein, numerical results for stimulated Brillouin scattering (SBS) in a step-index few-mode fiber are discussed based on the theory of wave optics and a mathematical model of SBS in a single-mode fiber. The acousto-optic coupling coefficient is calculated and a series of Brillouin gain spectra and phase shift spectra are presented according to the optical and acoustic mode profiles. Numerical results demonstrate that acoustic modes involved in the SBS process are primarily those with low mode orders. Compared to inter-mode SBS in LP01 and LP11 modes, intra-mode SBS is more critical, wherein the latter can obtain larger Brillouin gain and phase shift. In addition, the Brillouin frequency shift evidently decreases as the optical mode order increases.