Wideband stimulated Brillouin scattering (WSBS) and forward stimulated Raman scattering (FSRS) in water pumped by a multi-longitudinal-mode laser are studied. The experimental results indicate that in the pump process of multi-longitudinal-mode laser, energy changes exist between WSBS and FSRS. WSBS will be dominant when the focal length is shorter or the pump energy is lower; on the contrary, FSRS will be dominant with the increase of focal length and pump energy or the appearance of optical breakdown.