Based on orthogonal dual-pump four wavelength mixing in an semiconductor optical amplifier，theorectical model of all-optical wavelength conversion for polarization multiplexing quadrature phase shift keying signals was set up for studing the characteristics of wavelength conversion for polarization multiplexing phase-modulated signals. The simulation system was built based on the theoretical analysis. Results show that the frequency spacing between the pump and signal lightwave, the polarization angle between pump1 and one of the polarization multiplexing signals have effects on the converion efficiency and the quality of the signals; and the phase noise generated by cross phase modulation in wavelength conversion also has effect on the quality of the signals, and when the power of two pumps is much larger than that of the signal lightwave, the cross phase modulation has small effect on the quality of the signals. The simulation results are consistent with the theoretical analysis. The methods and some results can be useful to research wavelength conversion system for other polarization multiplexing signal based on four wavelength mixing in SOA.