The reflection spectra of polarization-mode conversed light in Magnetooptic Fiber Bragg Gratings (MFBGs) dependent on the magnetooptical coupling intensity is investigated.According to the magnetooptic coupled-mode theory combined with the propagation property of fiber Bragg grating,the magnetic control characteristics of the MFBGs are analyzed numerically.The 3 dB bandwidth tunable filter is obtained by adjusting the magnetooptical coupling intensity.The clock extraction of 40 Gbps RZ data signal by utilizing the comb filtering of MFBGs under bias magnetic fields is simulated and the jitter performance of the MFBGs is also analyzed.