Abstract: In response to the problems of small pressure monitoring range, low sensitivity, and high cost of existing fiber optic pressure sensors, an improved fiber optic pressure sensor is designed. A strain fiber optic grating is stuck on the cantilever beam and a temperature fiber optic grating is suspended (to make it stress free). The limit cover below the cantilever beam places the spring, corrugated pipe pressure cover, and corrugated pipe cover inside it. The inner upper plane of the limit cover contacts the upper plane of the spring, and the lower plane of the spring contacts the corrugated pipe pressure cover. When external pressure reaches the corrugated pipe through the pipeline at the bottom of the corrugated pipe, the high pressure causes it to undergo axial deformation. The deformation in turn compresses the spring. Finally, the spring undergoes deformation and transmits force to the cantilever beam, changing the stress situation of the strain grating. A spring with a larger stiffness coefficient is added to the single-layer corrugated pipe to limit its deformation when external pressure is generated, allowing the corrugated pipe and spring to jointly transmit pressure to the cantilever beam. The experimental test results show that the improved sensor has a pressure monitoring range of 0-5 MPa, which is 5 times higher than before. The sensitivity of the sensor is 0.379 98 nm/MPa, and the measurement error is within 0.02 MPa. The improved pressure sensor is validated in a water pipeline underground. The results show that compared with the measurement results of high-precision electronic pressure gauges, the pressure demodulation error of the sensor is within 0.02 MPa.