Thermal modeling of the power transformer to estimate the internal temperature only reflects the winding hot spot to a certain extent. The application of optical fiber sensors to measure transformer internal temperature directly can obtain the true temperature with high accuracy and stability and overcome the shortcomings of traditional electric sensors. It analyses the measuring principle of FBG(fiber bragg grating)sensor, and constructs transformer internal temperature measurement platform with FBG temperature sensors, then adopt short-circuit method to simulate the process of winding heat under different load conditions. Finally the measurement of transformer internal temperature is conducted respectively with FBG temperature sensors and thermoeouples. Comparison and analysis of the results shows that FBG sensors can effectively measure the internal temperature of the transformer.