In　this　paper,　we　consider　a　discrete　Lotka-Volterra　competitive　system　with　the　effect　of　toxic　substances　and　feedback　controls.　By　using　the　method　of　discrete　Lyapunov　function　and　by　developing　a　new　analysis　technique,　we　obtain　the　sufficient　conditions　which　guarantee　that　one　of　the　two　species　will　be　driven　to　extinction　while　the　other　will　be　permanent.　We　improve　the　corresponding　results　of　Li　and　Chen　[Extinction　in　two-dimensional　discrete　Lotka-Volterra　competitive　system　with　the　effect　of　toxic　substances,　Dynam.　Contin.　Discrete　Impuls.　Syst.　Ser.　B　Appl.　Algorithms　15　(2008)　165-178].　Also,　an　example　together　with　their　numerical　simulations　shows　the　feasibility　of　our　main　results.　It　is　shown　that　toxic　substances　and　feedback　control　variables　play　an　important　role　in　the　dynamics　of　the　system.