A novel demodulation technique for magnetic field fiber Bragg gratings (FBG) sensors based on the monitoring of the polarization dependent loss (PDL) in transmission is presented. Theoretical simulations are realized using the coupled mode theory. It is shown that in certain range the PDL peak value increases with applied magnetic field monotonously. The effects of grating parameters on measurement range and sensitivity are analyzed. The experimental measurements are conducted on FBG inscribed by means of the phase mask technique. A good agreement between experimental and simulated evolutions is demonstrated. Owing to the polarization properties it is possible to obtain temperature and axial strain-insensitive measurements which is demonstrated by theoretical study and experimental measurements.