Through focusing Q-switched laser pulses into FC-72 medium, the intensity profile of backward stimulated Brillouin scattering (SBS) spot is investigated experimentally by charge-coupled device (CCD) camera and digital image processing technology, and the rules of intensity profile and spot size versus pump energy are obtained. The results show that the intensity profile of backward SBS spot turns from quasi-Gaussian to Gaussian profile when the pump energy increases. And the size of SBS spot decreases gradually in a whole with pump energy. When pump energy is near the SBS threshold, the size of SBS spot is maximum, and larger than that of pump spot. When pump energy is three times larger than the SBS threshold, the size of SBS spot is minimum and smaller than that of pump spot.