A　1　:　8　scale　model　of　a　double-layer-island　subway　station　with　full-high　security　doors　was　built.　Through　model　experiments,　smoke　flow　characteristics　in　track　and　public　areas　were　studied　when　fire　broke　out　in　one　end　of　track　area.　The　results　show　that,　when　the　fire　is　at　the　growth　stage,　if　the　mechanical　extraction　system　stops,　the　smoke　in　track　area　will　diffuse　to　the　public　area　through　the　space　at　the　top　of　full-high　security　doors　and　blocks　the　evacuation　path　of　stairway　near　the　fire　source.　When　the　mechanical　extraction　system　runs,　the　velocity　of　smoke　diffusing　to　the　public　area　can　be　controlled　obviously.　But　due　to　the　nonuniformity　of　extraction　characteristics　of　vents　in　the　track　area,　the　smoke　in　the　track　area　will　overflow　to　the　public　area　through　the　space　at　the　top　of　full-high　security　doors　near　the　fire　source　away　from　the　fans.　If　smoke　flow　rates　of　vents　are　uniform,　smoke　will　be　well　controlled　from　diffusing　to　the　public　area.