According to the nonreciprocal characteristic of magnetooptic material and the filtering characteristic of waveguide grating, the nonreciprocal filtering characteristic and the application of magnetooptic waveguide grating are presented. YIG crystal doped by Ce (Ce:YIG) with Faraday rotation angle (ΘF) of 4800 °/cm, rib section of compensation wall of single mode and apodizer grating of cosine type are chosen to design the magnetooptic waveguide grating. The method of finite-difference and equivalent effective index are used to simulate the intensity of the nonreciprocal effect of the magnetooptic waveguide grating. Besides, coupled-mode theory and transfer matrix method are also used to analyze the nonreciprocal filtering characteristics of the magnetooptic waveguide grating. The result indicates that for transverse electric (TE) mode and the wave band of 1550 nm, the forward center-wavelength of the magnetooptic grating is shifted by 0.8 nm relative to the backward center-wavelength and the bandwidth is 0.4 nm (-20 dB). This kind of nonreciprocal filtering characteristic can be applied to integrated optical devices such as nonreciprocal isolator and optical add-drop multiplexer (OADM).