An exhaust turbocharging system makes it possible to increase the brake mean effective pressure (BMEP) and lower emissions levels for a diesel engine while further improving the thermal efficiency. However, in order to meet future emission regulations, further reductions in NOx and particle matter (PM) emissions are necessary. In addition, the diesel engine should have further reductions in fuel consumption to reduce CO₂, which is one of the main greenhouse gases.Authors participated in a program for the comprehensive technological development of innovative, next-generation, low-pollution vehicles with the New Energy and Industrial Technology Development Organization (NEDO) from 2004 through 2008 in cooperation with the National Institute of Advanced Industrial Science and Technology (AIST). A low-emission and high-efficiency diesel engine system was developed to meet the target of NEDO project.The turbocharging system which makes possible the high boost and high exhaust gas recirculation (EGR) rate was evaluated by using simulation. Thus, the sequential three-stage turbocharging system was proposed and the engine that was equipped with this turbocharging system was tested. Finally, the project target was achieved by the three-stage turbocharging system with the combined use of the exhaust aftertreatment system. This paper describes the simulation evaluation of the turbocharging systems, which was developed as an elemental technology in the NEDO project, and test results on the improvement in the tradeoff between NOx emission and fuel consumption.