A high-sensitivity optical fiber Fabry-Perot (F-P) temperature sensor based on the harmonic vernier effect (HVE) is proposed and fabricated to achieve high-sensitivity temperature measurements. The sensor consists of two parallel F-P interferometers formed by single-mode fiber (SMF)-air-SMF and SMF-polydimethylsiloxane (PDMS)-SMF, where the air cavity serves as the reference cavity and the PDMS cavity serves as the sensing cavity. By changing the length of the reference cavity and paralleling it with a sensing cavity of the same length, sensors 1 and 2 are fabricated for temperature-sensing experiments based on the traditional vernier effect (TVE) and HVE, respectively. Experimental results show that within the temperature range of 31?35 °C, the temperature sensitivity of a single sensing cavity is 1.640 nm/°C. The temperature sensitivities of sensor 1 based on TVE and sensor 2 based on HVE reach -5.125 nm/°C and 16.025 nm/°C, respectively, which are 3.12 and 9.77 times of that of a single sensing cavity. Compared with single and TVE sensors, the HVE sensor can achieve higher temperature sensitivity. Moreover, the sensor is easy to fabricate and can satisfy different temperature requirements, which thereby exhibits broader application prospects.