Our investigation indicates that if the incident laser contains distinct pre-pulse, the occurrence of stimulated Brillouin scattering under the interaction of high intensity sub-ns pulse laser with plasmas can be self-consistently confirmed. The evidences include an anomalous increase of the fraction of incident laser energy which is backscattered into the focusing lens, the red shift and broadening of spectrum of back-reflected laser, the dramatic reduction of total ion energy and fast ion emission, the enhancement of sidescattered laser light at large scattering angles and so on.