In　order　to　meet　NOx　limitation　of　the　atmospheric　regulations,　it　is　necessary　to　control　the　volumetric　NOx　concentration　at　the　main　tail　pipe　of　the　test　bench　group.　According　to　both　the　site　dimension　of　the　test　bench　group　and　the　operating　characteristic　of　the　engine　test,　this　work　proposed　a　method　that　each　test　bench　adopts　a　selective　catalytic　reduction(SCR)　system　to　deal　with　NOx　emissions　of　the　diesel　engine,　and　a　distributed　control　technology　was　used　to　coordinate　the　SCR　conversion　efficiency　of　each　test　bench　according　to　the　NOx　emission　level　in　the　main　tail　pipe.　Two　indexes　were　proposed　in　which　one　is　the　control　difficulty　coefficient　for　a　single　test　bench　and　the　other　is　the　integrated　control　difficulty　coefficient　for　the　test　bench　group.　In　addition,　the　optimization　objective　is　to　minimize　the　integrated　control　difficulty　coefficient　to　coordinate　the　real-time　NOx　conversion　efficiency　of　each　test　bench.　This　technical　proposal　was　verified　in　a　practical　test　bench　group　containing　several　diesel　engines　by　successfully　reducing　NOx　emissions　in　the　common　main　tail　pipe　to　meet　the　limit　requirement.　©　2022,　Editorial　Office　of　the　Transaction　of　CSICE.　All　right　reserved.