A comprehensive broad-band dynamic model of nearly degenerate four-wave mixing (FWM) in semiconductor optical amplifier (SOA), in case of the polarization states of two input lights being not parallel, is presented. By numerical simulation, take the all-optical wavelength conversion based on nearly degenerate FWM in an SOA for an example, the effects of two input light powers, frequency detuning and polarization angle of two input lights on the nearly degenerate FWM and the performances of wavelength conversion are theoretically investigated. The results indicate that there exist the optimal powers of two input lights. As the frequency detuning between the two input signals and the polarization angle of two input lights increase, the conversion efficiencies are decreased. The polarization state of C13 becomes larger as the polarization angle of two input lights increases.