In the chromatographic tracing analysis of main transformer oil in a power station,the total hydrocarbon content was found a sudden increase for three times.By using the threeratio and graphical analysis method of chromatographic analysis data,the type of the fault was determined to be the temperature overheating.Oil filtering process and special operation and maintenance strategies were carried out according to the analytical result.The main transformer is running well and the chromatographic data of the transformer oil is normal after the treatment methods mentioned above.