A novel real-time pressure measurement using Stokes parameter of fiber Bragg gratings (FBG) in transmission is proposed. It is analyzed that the first Stokes parameter of the transmitted light in FBG has monotonous relationship with linear birefringence induced by pressure. The simulations show that the choices of incident angle and the wavelength points have an important effect on the sensitivity, the linearity of the sensor and dynamic range. Experimental results obtained on fiber Bragg gratings transversally loaded by an external force confirm the simulated evolutions. The performances are analyzed and the solutions are proposed to improve the system.