A　two　species　non-autonomous　competitive　phytoplankton　system　with　Beddington-DeAngelis　functional　response　and　the　effect　of　toxic　substances　is　proposed　and　studied　in　this　paper.　Sufficient　conditions　which　guarantee　the　extinction　of　a　species　and　global　attractivity　of　the　other　one　are　obtained.　The　results　obtained　here　generalize　the　main　results　of　Li　and　Chen　[Extinction　in　two　dimensional　nonautonomous　Lotka-Volterra　systems　with　the　effect　of　toxic　substances,　Appl.　Math.　Comput.　182(2006)　684-690].　Numeric　simulations　are　carried　out　to　show　the　feasibility　of　our　results.