In　view　of　the　problem　that　IEC　three　ratio　method　has　the　disadvantage　of　absolute　boundary　and　lack　of　codes,　a　novel　transformer　fault　diagnosis　method　based　on　generalized　regression　neural　network　(GRNN)　and　Fuzzy　C-means　(FCM)　clustering　algorithm　is　proposed　and　a　GRNN-FCM　combined　transformer　fault　diagnosis　model　is　constructed.　Five　volume　fractions　of　the　gases　in　oil　and　its　three-ratio　codes　are　chosen　to　be　the　inputs　of　the　combined　model.　This　model　uses　GRNN　model　to　judge　the　preliminary　fault　type　(normal,　overheat,　discharge,　discharge　&　overheat),　then　Fuzzy　C-means　clustering　algorithm　is　adopted　to　achieve　the　transformer　fault　diagnosis.　After　comparing　the　combined　model　to　other　two　diagnosis　methods,　the　simulation　results　indicate　that　this　combined　model　has　accordant　outputs　with　the　measured　values　and　provides　higher　accuracy,　so　the　feasibility　and　effectiveness　of　the　model　presented　are　verified.　©　2016,　Xi＇an　High　Voltage　Apparatus　Research　Institute　Co.,　Ltd.　All　right　reserved.