Abstract - The dissolved gas analysis (DGA) is an effective technique for detecting incipient faults in oil-immersed power transformers. So the paper investigates the DGA methods, while employ the ANSI/IEEE C57.104 standards and the Key Gas diagnosis rules as based on to develop a fast transformer fault diagnosis method in practice. We designed a report’s form which was so easy understand that we can accurate of diagnosis what was up in the body of transformer by EXCEL programmed. The user only keys in the measured data of main gases including CO, H2, CH4, C2H2, C2H4, and C2H6 those gases were taken from ASTM D3612’s instruction. Then the diagnosis result was showed in texts and the plotted figures which were two figures to compare diagnosis the test’s figure with the reference figure that was taken the analysis of transformer fault from over past in power system. The proposal offers a simple, a quick, and an accurate of diagnosis through human - machine interface, while which was quickly, simply, and accurately proved on October 25th, 2012 Nan Cou E/S #4 ATr’s insulating oil of diagnosis.