The　vaned　diffuser　profile　designed　preliminarily　has　been　optimized　using　artificial　neural　network　and　genetic　algorithm　under　stage　environment　to　improve　the　aerodynamic　performance　at　the　design　operation　condition.　The　aerodynamic　performance　of　the　stage　composed　of　the　vaned　diffuser　optimized　and　the　original　impeller　at　the　design　and　off-design　operation　conditions　is　predicted　using　the　numerical　method.　The　results　show　that　the　static　pressure　recovery　coefficient　of　the　vaned　diffuser　and　the　isentropic　efficiency　of　the　stage　was　increased　by　11.7%　and　1.64%,　respectively.　The　total　pressure　loss　coefficient　of　the　vaned　diffuser　was　decreased　by　21.12%,　and　the　isentropic　efficiency　of　the　stage　was　86.1%　at　the　design　operation　condition.　Moreover,　the　aerodynamic　performances　of　the　stage　at　the　off-design　operation　conditions　was　improved　significantly.　In　addition,　the　surge　margin　of　the　stage　was　increased,　and　the　choke　margin　was　decreased　slightly.