Abstract: Pressure sensor is a key element for pressure supervising during industrial production. The mathematical relations between the central wavelength and the strain of optical fiber grating were analyzed. The mathematical relations between the deflection of central diaphragm and the pressure were analyzed when the circular flat diaphragm with rigid center was in uniform compression. A circular flat diaphragm was designed as the sensing element of fluid pressure and the converter to transfer the fluid pressure to optical fiber grating. The optical grating sensor was assembled with secondary element and the linear mathematical model of the input and output of the sensor was built. The linearity and repeatability of the sensor were demonstrated by experiments. The parameters of the optical fiber grating pressure sensor were got using mathematical computing. The sensitivity of the optical fiber grating pressure sensor is -0.658 nm/MPa, and the initial wavelength is 1 578.441 nm. This research paves the way for the further stability of the sensor.