From　the　point　of　view　of　practical　application,　a　hierarchical　reduction　approach　of　the　rough　sets　theory　is　proposed.　In　this　approach,　according　to　the　acquisition　mode,　cost　and　the　real　time　requirement,　the　attributes　are　classified　to　different　parts　allocated　at　several　layers.　So　the　knowledge　in　information　systems　or　decision　systems　can　be　presented　hierarchically　with　multiple　granularities　at　multiple　layers.　And　the　reduction　can　hierarchically　be　applied　to　part　of　attributes　allocated　at　each　layer.　On　the　information　theory,　the　basis　of　this　approach　is　proved.　Furthermore,　the　properties　of　this　approach　are　discussed,　such　as　practicability,　rapidity　and　good　dynamic　performance.　Finally,　in　acquiring　the　control　decision　of　a　cement　kiln,　the　hierarchical　reduction　approach　shows　its　validity.