In the system of magnetic field measurement based on the polarization properties of fiber grating, the polarization dependent loss (PDL) is influenced by the structure of fiber grating. From the principle of the measurement system, the bandwidth and slope of transmission spectrum corresponding to the measurement range and sensitivity respectively which relate to the grating structure are analyzed. The measurement performance on uniform, phase shifted, and logarithm-triangle fiber gratings is simulated, which shows that the logarithm-triangle fiber grating can broaden the bandwidth of PDL peak values and improve the measurement responsibility. The experiment with logarithm-triangle fiber grating designed by the technology of reconstruction equivalent chirp is implemented, and the result provides reference for grating structure selected in the measurement system.