In　industrial　application,　an　engine　group　with　several　engines　running　in　parallel　produces　emissions,　and　because　of　its　variable　operation　conditions　and　the　number　of　engines　being　run,　it　produces　great　pollution.　This　study　proposes　a　distributed　control　system　(DCS)　method　to　deal　with　NOx　emissions　from　a　diesel　engine　group.　This　DCS　method　contains　several　diesel　engine　test　benches　in　parallel,　and　each　engine　is　connected　to　an　independent　DCS　unit　with　a　selective　catalytic　reduction　(SCR)　device,　and　the　central　processing　unit　(CPU)　distributes　controlling　quantities　to　each　DCS　unit.　A　dimension-less　parameter,　coefficient　of　difficulty　K,　is　introduced　to　evaluate　the　NOx　conversion　efficiency　of　each　unit.　A　control　algorithm　adopting　the　minimum　K　as　the　optimization　control　object　to　distribute　the　real-time　NOx　conversion　efficiency　for　each　unit　is　presented.　This　DCS　deNOx　technology　has　been　applied　in　10-engine　test　benches　in　parallel,　and　the　results　show　that　the　DCS　method　not　only　controls　NOx　emissions　of　the　engine　group　within　the　emission　standard　limit　but　also　exhibits　a　good　economic　performance　for　suitable　NOx　conversion　efficiency　distribution　and　economical　urea　injection　dose.　This　DCS　emission　control　method　is　suitable　for　multiple　diesel　engines　running　in　parallel　under　conditions　of　varied　speeds　and　loads.