The reflection characteristics of few mode fiber Bragg grating (FM-FBG) with non-uniform profile of index change were numerically studied. The reflection spectrum of FM-FBG was obtained by solving the coupled mode equation using shooting method. Under the condition that the maximum index change at the core-cladding interface and absorption coefficient were constant, the numerical results indicated that the reflectivity of cross-mode coupling peak between LP_ 01 and LP_ 11 modes varies parabolically with the saturation length of index change. When saturation length was small, the reflectivity of cross-mode coupling increased with saturation length and reached a maximum value. With the further increasing saturation length,the reflectivity of cross-mode coupling decreased gradually to zero when saturation length increased to the diameter of fiber core. It was also indicated that the peak reflectivities, which correspond to forward modes coupled to the same order back-ward modes, increased monotonically with saturation length.