All-optical wavelength converter can avoid wavelength conflict in wavelength division multiplexing channels, thus improving the transmission efficiency and increasing the network flexibility and capacity in all-optical networks. All-optical wavelength converter has become the research hotspot in recent years. Semiconductor optical amplifier (SOA) is the preferred choice for all-optical wavelength converter device. In the scenario of strict transparent all-optical network transmission, the all-optical wavelength converter utilizing the four-wave mixing effect of SOA is considered of greatest research value. A 40 Gb/s return-to-zero differential phase shift keying (RZ-DPSK) all-optical wavelength converter simulation system is built up based on four-wave mixing effect of SOA by OptiSystem software. With the aim to obtain higher conversion efficiency, higher optical signal-to-noise ratio and lower power penalty, the best parameters and best working environment are presented based on the discussion of the relationship among the parameters including injection current to SOA, wavelength detuning, signal and pump power.