This article proposes and demonstrates a fiber optic sensor based on two cascaded Fabry-Perot interferometers (CFPIs) for simultaneous measurement of temperature and pressure. The sensor is made by fusion splicing of the single-mode fiber (SMF), hollow-core fiber (HCF), and double-hole fiber (DHF) in sequence. An air cavity FPI is formed in HCF and a silica cavity FPI is formed in DHF. The two FPIs are cascaded to form the mixed cavity FPI. The air cavity FPI is connected with the external environment via holes in the DHF, realizing sensing of air pressure with high sensitivity. At the same time, due to the thermo-optical effect and thermal expansion effect of the silica in the DHF, high sensitivity sensing is realized for temperature. In this article, in the air pressure measurement range of 0.1?0.6 MPa and the temperature measurement range of 60?260 °C, the sensitivity of the air cavity FPI to air pressure and temperature is 4 nm/MPa and 1 pm/°C, respectively, and the sensitivity of the mixed cavity FPI to air pressure and temperature is 0.5 nm/MPa and 9 pm/°C, respectively. The air cavity FPI and the mixing cavity FPI have different sensitivities to temperature and air pressure, and realize the dual parameter measurement of temperature and air pressure. At the same time, the sensing structure has simple manufacturing process, high integration, and high sensitivity.