In order to study the influences of DOC, CDPF and SCR combination on power performance,fuel economy and emission performance of lightduty diesel engine,the bench test was conducted on a China V lightduty diesel engine with the after treatment system. The results showed that the addition of DOC, CDPF and SCR after treatment system had some effects on power performance and fuel economy of diesel engine,which were an average torque drop of 1.3% and an average fuel consumption rate increase of 2.6%. In addition, the after treatment system consisting of DOC, CDPF and SCR could reduce the NOx,THC, CO and PM emissions effectively. DOC could promote not only the purification of THC and CO,but also the reduction of PM. SCR mainly helped the purification of NOx,but the conversion efficiency was low at low exhaust gas temperature. CDPF was responsible for the purification of PM emissions and had a higher purification efficiency for PM with the medium and small particle diameter. The average reduction rates of PN and PM were 99.1% and 96.6% respectively.