The polarization maintaining fiber grating (PM-FBG) can be used as a multi-parameter sensor due to the inherent birefringence. In this paper, the spectral characteristics of PM-FBG under lateral pressure are analyzed. The experimental device is set up to measure the reflection spectra of PM-FBG with different lateral pressure and loading angles. The experimental results show that the applied stress perturbation will change the intrinsic birefringence axis of the polarization maintaining fiber and change the effective refractive index of the fast and slow axis. So the PM-FBG can be used as pressure sensor by measuring the shift rate of the reflection spectra.