Suppression of the stimulated Brillouin scattering (SBS) is an important technology for realization of fiber parametric amplification. Phase modulation is employed in the early literatures to meet this purpose. A new method is proposed that a secondly phase modulation is applied on a modulated optical source. Based on this technique, by adding a 365 MHz phase modulation to the 2 GHz phase modulated laser source, the stimulated Brillouin scattering threshold is improved from 10 dBm to 23.5 dBm. Continuous wave (CW) pump optical parametric amplification is demonstrated experimentally in a 1450 m-long highly nonlinear fiber (HNLF), with the nonlinear coefficient γ=11.9 W-1km-1, dispersion slope S=0.0155 ps/(nm2?km). Using an external cavity laser (ECL) as the signal, 26 nm bandwidth (gain>10 dB) and 24 dB maximum gain for small signal are obtained.