The　growth　of　plasma　electrolytic　oxidation　(PEO)　coating　at　initial　stages　is　relevant　directly　with　coating＇s　morphologies　and　properties.　In　this　work,　the　PEO　coating　on　Al　was　carried　out　at　a　constant　current　model　in　an　electrolyte　containing　sodium　silicate　and　potassium　hydroxide.　The　morphology,　the　phase　compositions　and　the　structures　of　initial　stages　PEO　coatings　were　examined　by　detailed　microstructural　characterization.　The　result　showed　the　PEO　coating　anodizing　＜11　s　exhibited　typical　characteristics　of　the　parallel-sided　pores　and　the　concave　Al/coating　boundary,　with　a　significant　temperature　rising.　After　that,　the　dielectric　breakdown　occurred,　resulting　in　many　micron-size　pores　formed　in　the　PEO　coating.　When　anodizing　time　over　15　s,　the　gas　discharge　appeared　at　the　coating/electrolyte　interface.　A　plasma-modified　layer　was　found　composed　of　gamma-Al2O3　nanoparticles　and　amorphous　materials　covering　the　coating　surface　to　prevent　the　coating　from　being　breakdown　by　electrons　in　the　plasma.　After　10　min,　the　PEO　coating　transforms　into　the　typical　porous　ceramic　PEO　coating.　This　study　is　helpful　in　the　design　of　the　new　functional　surface　of　the　PEO　coating,　as　well　as　the　deep　understand　of　the　coating　growth　mechanism.