Statistical　quantity　in　turbulence　and　turbulence　structure　were　investigated　by　direct　numerical　simulation　on　turbulent　flow　triggered　by　different　mechanisms　in　a　vertical　channel.　The　statistical　results　for　forced　convection,　combined　convection　and　natural　convection　include　mean　streamwise　velocity,　mean　temperature,　intensity　of　fluctuating　velocity　and　temperature,　Reynolds　stress,　and　turbulent　structure.　The　results　show　that:　Compared　with　forced　convection,　for　combined　convection,　buoyancy　leads　to　the　higher　mean　velocity　and　lower　intensity　of　velocity　fluctuation　near　hot　wall,　but　the　lower　mean　velocity　and　higher　intensity　of　velocity　fluctuation　near　the　cold　wall;　buoyancy　results　in　the　stronger　temperature　fluctuation　near　the　wall　regions　and　the　weaker　temperature　fluctuation　in　the　central　part　of　the　channel.　Compared　with　forced　convection　and　combined　convection,　for　the　natural　convection,　the　profile　of　the　mean　velocity　is　antisymmetric　to　the　center　line,　and　both　the　largest　velocity　fluctuation　and　the　smallest　temperature　fluctuation　occur　in　the　central　part　of　the　channel;　the　maximum　value　of　Reynolds　stress　also　locates　in　the　central　part　of　the　channel,　and　negative　Reynolds　stresses　are　near　the　walls.