The transmission and polarization properties of circular birefringence fiber gratings are analyzed. Based on the Jones matrix and the coordinate conversion, the evolutions with wavelength of transmission spectrum and the polarization properties of output light with different magnetic field intensities, grating lengths and incident states of polarization (SOP) are analyzed. The results show that circular birefringence leads to the splitting of transmission spectrum and variation of transmitted SOP for different wavelengths. It is demonstrated that the polarization-dependent loss (PDL) and the third Stocks parameter increase monotonously with applied magnetic field, and they can be used in magnetic field sensor. The measurement range and sensitivity are dependent on the grating structure and material. The dynamic measurement range of Bi-YIG and YIG fiber gratings are both given.