Abstract: Urea-SCR catalytic converter can effectively reduce the NOx emission of diesel engines, but meanwhile catalytic converter will cause some pressure loss in the exhaust system, which has negative influences on the engine performances. With the aid of BOOST (engine cycle simulation software) coupled with FIRE (computational fluid dynamic software), the pressure loss caused by converter was calculated and a modeling simulation and validity test were conducted on the power performance and fuel economy of diesel engine with urea-SCR catalyst. The results show that the pressure losses mainly come from the monolith resistance along the converter. The exhaust back pressure rising caused by SCR catalyst has some influence on the diesel fuel economy and power performance, which are reduced by about 5%. The results can provide a reference for optimum design of SCR catalytic converters and assembling.