Abstract: A urea injection control strategy for SCR system based on ammonia storage model was developed for a type of 6-cylinder high pressure common rail diesel engine.By modifying the conversion efficiency and urea injection amount with ammonia storage capacity, the precise control of urea injection amount was realized.The test results show that the steady-state cycle NO_x emission of bench test is 1.132 g/（kW·h）,and the transient cycle NO_x emission is 1.639 g/（kW·h）,both of which are lower than the four-stage regulations of non-road countries.At the same time, the urine-fuel ratio of this control strategy reached 5.56%,which improved the economy and effectively reduced the risk of urea crystallization compared with open-loop control.