In recent years,with the gradual increase of large capacity transformer and voltage level,the structure of the transformer has become more complicated. The leakage magnetic flux of the transformer is more and more big,and the magnetic flux leakage problem is more and more obvious. It is difficult to meet the requirement of measuring the internal temperature of the transformer by using the conventional electrical signal sensor. An optical fiber Bragg grating (FBG) temperature sensing intelligent test platform is developed for the analysis of magnetic flux leakage loss in transformer. The collected field measurement data are processed and analyzed in detail. The temperature rise of fuel tank top is 49.6 K and temperature rise of clamping piece is 58.3 K at 18∶36;the temperature rise of fuel tank top is 36.7 K and temperature rise of clamping piece is 36.8 K at 2∶45. Through the comparison and analysis of the magnetic flux leakage loss in the main parts,the conventional electrical signal sensor measurement method has been improved.