Abstract: Based on the nonlinear coupled mode equation governing the pulse evolution in fiber Bragg gratings (FBG), the Bragg wavelength shift near the forbidden band caused by nonlinear optical characteristics was analyzed numerically. A simulation model was established to study the switching performance of FBG for different input powers. The simulation result shows that the Bragg wavelength of the grating moves to longer wavelength, the reflection peak decreases and the bandwidth becomes narrow when the input signal power increases. The characteristics of the all-optical switch based on this effect were investigated. And it shows that the stabilization period of the switch is short and the pulse wave-shape remains undistorted.