According to the wave equation used when the optical pulse propagation in the fiber, the nonlinear coupled equation is a deduced under the joint actions of Raman effect and parametric amplification in the birefringent. with Lorentzian model of parallel Raman gain spectrum, the gain is obtained by combining the Raman effect and the parametric amplification when the pump wave polarization is oriented at 45 between the birefringent fiber axes. The gain spectrum is discussed as a function of the input parameters (input power, the group velocity mismatch) in different dispersion regimes. The result shows that Stokes and anti-Stokes gain spectra are asymmetric because of Raman effect. The gain appears as primarily anti-Stokes wave in anomalous dispersion regime, and Stokes wave in normal dispersion regime.