The　phase　composition,　morphology,　element　distribution　and　corrosion　resistance　of　surface　insulation　coating　on　the　oriented　silicon　steel　were　investigated　in　detail　using　X-ray　diffraction　(XRD),　scanning　electron　microscopy　(SEM),　energy　dispersive　spectroscopy　(EDS)　and　electrochemical　workstation,　respectively.　The　results　show　that　the　structure　of　the　insulation　coating　is　double　compound　layer.　The　bottom　layer　is　Mg2SiO4　phase　with　0.8　μm　thickness.　The　top　layer　is　AlPO4　phase　with　1.4　μm　thickness.　There　is　a　diffusion　area　with　0.4~0.6　μm　thick　at　the　junction　of　two　layers.　In　comparison　to　the　sample　coated　single　Mg2SiO4　layer,　the　sample　coated　double　compound　layer　exhibits　higher　corrosion　potential,　higher　polarization　resistance　and　lower　corrosion　current　density,　thus　leading　to　better　corrosion　resistance.　With　the　increase　of　immersion　time,　the　corrosion　solution　gradually　permeates　into　the　insulation　coating　and　reaches　the　silicon　steel　substrate,　and　then　reacts　with　the　substrate.　The　corrosion　process　can　be　divided　into　three　stages.　©　2016,　Beijing　Institute　of　Aeronautical　Materials　(BIAM).　All　right　reserved.