Aimed　at　the　diesel　engine,　a　selective　catalytic　reduction　(SCR)　system　was　developed.　In　this　system,　the　urea　pump　is　integrated　with　a　urea　tank,　air　and　urea　mix　in　the　injector,　catalyst　convertor　is　based　on　vanadium.　Combining　with　a　self-developed　control　unit,　the　urea-SCR　system　was　tested　on　the　engine　bench.　The　ESC　experiment　results　indicate　that　the　NOx　emission　can　be　reduced　effectively　which　meets　the　China　stage　IV　regulation.