In order to achieve simultaneous temperature and strain measurement, in this paper, a fiber optic temperature and strain sensor based on multi-mode interference is proposed. The sensor is fabricated by splicing a section of thin polarization maintaining fiber and a piece of thin core fiber in a Sagnac loop with a fiber fusion splicer. Interference between polarization modes and core mode-high cladding modes exist in the sensor due to fiber offset and mode field diameter mismatch. The transmission spectra corresponding to the two types of interferences under different temperatures and strains are extracted by a low pass filter. The simultaneous temperature and strain measurement are validated by building a matrix through the temperature and strain sensitivities of two selected dips in transmission spectra. Experimental results show that the temperature and strain resolutions are 0.30 ℃ and 13.50 με, respectively. This experiment can be used as an innovative physics experiment for undergraduates majoring in physics and optoelectronics to help them master the principles of optical fiber sensing, experimental skills, and data processing and analysis methods.