Abstract: The new distributed optical fiber temperature sensor has unique advantages that electrical temperature sensor does not have. It greatly expands the application field of temperature measurement in vacuum low temperature environment. The distributed optical fiber temperature sensor is applied to measure the temperature gradient in vacuum under the environment of low temperature heat sink. The traditional thermocouple temperature sensor and the distributed optical fiber temperature sensor are placed in the same double aluminum plate structure. The aluminum plate and sensors are placed in vacuum under the environment of low temperature heat sink. Different temperature gradients in vacuum low temperature heat sink environment are realized by heating temperature control of aluminum sheet. The temperature data of aluminum plate measured by two kinds of sensors are analyzed. The results shows that the distributed fiber Raman temperature measurement system can accurately measure the temperature gradient in vacuum low temperature heat sink environment and meet the temperature measurement of workpieces under low temperature conditions.