Accurate insight of the condition of transformers is essential for all electrical networks and on-line monitoring of critical transformers has become increasingly important. The knowledge gained from closely monitoring expensive transformers can maximize its longevity and avoid expensive failures. On-Line Transformer Gas Analyzer represents a new generation of test equipment for analysis the dissolved gas in oil. IOD TGA adopted the advanced infrared photo-acoustic spectroscopy technology and the friendly operation interface. The concentration data of the 7 key fault gases and moisture can be drawn directly within 20 minutes in the field. It really can take place of the Gas Chromatography system in the laboratory because of the accurate, rapid, reliable results. Thus the IOD TGA is one of the best tools for the electric equipment asset evaluation.