A format conversion from a non-return-to-zero (NRZ) signal to return-to-zero (RZ) signal is presented based on four-wave mixing (FWM) and cross-phase modulation (XPM) in a silicon optical waveguide. When a NRZ signal acting as the probe and a periodic pulse train as the pump are launched into the silicon waveguide synchronously, the Stokes and anti-Stokes are generated by FWM and the red and blue shifts are induced by XPM in the probe spectrum. Four RZ signals can be then extracted by utilizing appropriate optical bandpass filters (OBPF). The power variations in the Stokes and anti-Stokes due to the change of pump and probe power, the relation between four RZ signal pulse widths and pump pulse width, and the influence of the wavelength detuning of pump to probe on the conversion efficiency etc. are investigated. Furthermore, the pump pulse width affects the qualities of XPM-induced RZ signals. When the pump pulse width ranges from 2 to 15 ps, four high-quality RZ signals can be obtained. And when the pulse width is larger than 15 ps, the RZ signal filtered from blue shift spectrum of the probe is of bad quality.