According to the sensing principle of FBG,the measurement performance of magnetic field sensor based on the differential group delay(DGD)in FBG is discussed in this article.The influence of external environmental parameters,including temperature,stress and pressure,on magnetic field sensor based on DGD are then analyzed from the aspect of theory and simulated through Matlab.As the simulation results indicates,the magnetic field sensing scheme based on DGD is not sensitive to temperature and stress,the specific performance is that the changing temperature or stress can make the DGD spectrum move along the horizontal axis(the wavelength),with the shape unchanged; when temperature variation or phase axial stress maintains the same,the DGD has a linear relation with the magnetic induction intensity.While the external pressure has serious impact on the magnetic field sensing scheme,which is apparently embodied in nonlinear and irregular change of DGD spectrum with the varying pressure.