An optical fiber temperature sensor comprising two Sagnac interferometers (SI) cascading is designed and experimentally demonstrated the temperature sensitivity amplification properties of the sensor under the vernier effect.The sensor consists of two SI with different length panda fibers,and then two SI rotates one angle to cascade together forming a temperature sensing device,where SI1 used as temperature sensing and SI2 as reference filter.Since the two SI have a similar free spectrum range,when they are cascaded,their output spectrum forming a low frequency envelope with the large free spectrum ranges.The sensitivity of amplification can realize when using the envelope drift to investigate the temperature changes.The experimental results show that the temperature sensitivity of the sensor is 11.03 nm/°C,while the temperature sensitivity of the single SI1 is 1.01 nm/°C.Therefore,after using the Vernier effect,the sensitivity increases by 10.9 times,and the experimental measurement results are in good agreement with the theoretical calculations.