A compact and highly sensitive gas pressure and temperature sensor based on Fabry-Pérot interferometer (FPI) and fiber Bragg grating (FBG) is proposed and demonstrated experimentally in this paper. The theoretical model for pressure and temperature sensing is established. Building on this foundation, a novel micro silicon cavity sensor structure sensitive to pressure is devised downstream of an FBG. The concept of separate measurement and the mechanisms enhancing pressure sensitivity are meticulously analyzed, and the corresponding samples are fabricated. The experimental results indicate that the pressure sensitivity of the sensor is −747.849 nm/MPa in 0—100 kPa and its linearity is 99.7% and it maintains good stability in 150 min. The sensor offers the advantages of compact size, robust construction, easy fabrication, and high sensitivity, making it potentially valuable for micro-pressure application.