A non-thermal plasma reactor was designed based upon dielectric barrier discharge theory. The non-thermal plasma assisted catalyst system was established with a Na-Rh/γ-Al2O3 catalyst system. The experiment was carried out and the reduction of diesel engine harmful emissions had been investigated with NPAC technology. Results showed that the particulate matter was reduced effectively and the maximum of soot removal efficiency was around 58%. The NOx emission was decreased remarkably by NPAC system. Under the low load conditions, the speed of 3 600r/min was corresponding to higher NOx conversion, and the maximum conversion was around 81.5%. Under the high load condition, the speed of 2 000r/min showed higher NOx conversion. 