A systematical approach was proposed to evaluate the impact of linear and nonlinear phase mismatch on tunable paiametric wavelength converts based on degenerate four-wave mixing in high-nonlinearity fibers.The result shows that,for any media fiber with a given dispersion wavelength,there exits a corresponding optimal signal wavelength,at which the tuning range can be maximized.Then the analytical expressions of the optimal signal wavelength and the maximum tuning range were deduced.Based on these expressions,a systematic optimization method was proposed to enhance the tuning range and minimized the gain ripple.