A fiber optic temperature sensor based on the multimode interference effect in the hollow core fiber(HCF) is proposed. which is a three section structure of single mode fiber - hollow core fiber - single mode fiber (SMF-HCF-SMF) ,A section of the HCF with an inner diamete of 5um and a length of 20mm. A broadband light source is used to illuminate the sensor structure , monitor the transmission spectrum of the sensor, and use the sensitivity of the sensor's multimode interference characteristic peak wavelength to temperature to realize temperature monitoring. The temperature rise experiment was conducted in the range of 30-80℃, and the temperature sensing characteristic with good linearity and sensitivity of 24.3pm/℃ was obtained. The proposed sensor has advantages of compact structure, simple manufacture, high reliability.