Under the same conditions, such as the powers of signal and pump, compared with single pump, the dual-pump produces higher optical parametric gain and broader gain bandwidth. As the signal gain characteristics directly interact with the parametric gain parameter, an optical parametric amplification (OPA) model is established based on highly nonlinear fiber (HNLF) with dual-pump, and the characteristics of phase matching condition, parametric gain and signal saturation gain are discussed. The time-domain finite-difference method is adopted to simulate the characteristics of saturation gain. The results indicate that parametric gain is related to fiber parameters, launched pump and signal wavelength and power, while the signal saturation gain is related to pump power.