In order to monitor the pressure and temperature changes in petrochemical reactor under high temperature and high pressure in real time and strictly control the reaction process of raw materials, an optical fiber Fabry-Perot (F-P) temperature and pressure composite sensor was designed and fabricated by using F-P multi cavity interference theory. The sensor was composed of quartz glass and sapphire glass. The air chamber between quartz and sapphire was pressure chamber, and the temperature chamber was sapphire itself. Through theoretical calculation and simulation verification, the effects of different parameters of pressure chamber and temperature chamber on the performance of the sensor were analyzed, and the best structural parameter data of the sensor were obtained. The results show that the sensor has simple fabrication process and reliable performance, and can realize the simultaneous measurement of pressure and temperature in the range of 0MPa~5MPa and -20℃~300℃. The experimental results show that the sensor has a good linear response relationship between pressure and temperature under the environment of pressure 0.1MPa~5MPa and temperature 20℃~180℃. The pressure sensitivity is 796nm/MPa and the temperature sensitivity is 3.864nm/℃. The sensor is suitable for simultaneous monitoring of pressure and temperature in high temperature and high pressure environment in petrochemical reactor.