Applying　the　rough　set　theory　make　the　controlling　quantity　roughened,　and　realizes　a　variable　precision　control.　The　result　of　study　reveal　that　the　information　of　control　system　can　be　conserved　by　roughen　the　controlling　quantity,　the　conversion　from　precision　quantity　set　to　smaller　amount　control　rules　can　be　achieved,　the　variable　precision　control　can　be　realized　by　the　means　of　equal　relative　error.　From　the　simulation　result　check,　it　can　be　achieved　that　make　the　system　moving　more　quickly　than　before　by　using　the　exponential　rough　set　controller　and　the　system　performance　can　be　satisfied　at　the　same　time.　So　that　it　is　an　effective　method　for　nonlinear　controller　design.