In this paper, we present a cascaded fiber Sagnac interferometer and fiber optic modal interferometer high sensitivity temperature sensor based on vernier effect and study the sensing properties experimentally.The fiber Sagnac interferometer consists of a section of polarization maintaining fiber fiber and 3 dB four-port coupler, and the fiber optic modal interferometer is formed by a fusion of few-mode fiber and two segments of single-mode fiber. Selected fiber Signak interferometer as temperature sensor and fiber optic modal interferometer as filter.By controlled the length of polarization maintaining fiber and few-mode fiber, the free spectral range of the optical fiber Sagnac interferometer is 2.63 nm, and the free spectral range of the optical fiber optic mode interferometer is 2.82 nm, and the free spectral range is similar and unequal, thus formed the optical vernier effect.The experimental results show that the temperature sensitivity of a single fiber Sagnak interferometer is -1.30 nm/℃, and after the cascaded of fiber mode interferometer, the temperature sensitivity increases to -18.19 nm/℃ with a magnification of 13.99.The sensor has a simple manufacturing process, good stability, and does not require special sensitization materials to improve sensitivity. Therefore, it has broad application prospects in fields such as chemical, medical, aerospace, etc.