Stimulated Brillouin Scattering (SBS) suppression is one of the key technology in optical fiber AM-CATV externally modulated transmission system. In this paper, a novel two signal phase modulation for SBS suppression is presented. The theoretical analysis and calculation have shown that the two signal phase modulation is more efficient than the single signal phase modulation for the increase of SBS threshold. The choice of frequency in two signal phase modulation is also analyzed and calculated in this paper.