Abstract: A new “double wall jet” combustion system was designed for improving the emissions and fuel economy performance of DI diesel engine. Effects of such operating condition as structure parameters of combustion chamber and injector, speed, load and injection timing on the combustion process of “double wall jet” were investigated by experimental method. The results showed: with the increasing of engine speed, the SOC was lagged off, the peak of combustion pressure showed a trendy of increasing firstly and reducing subsequently; the transient ROHR, meaning temperature of combustion and accumulated heat release, were reduced. With the increasing of load, the SOC was advanced; the angle of peak pressure was lagged off; the peak pressure, mean temperature of combustion and accumulated heat release were increased, while the indicated thermal efficiency was reduced. At engine speed of 2100 r/min, the combustion duration of double-wall-jet combustion system was mainly affected by compression ratio at lower load, but mainly affected by the amount of pre-mixed combustion at higher load. The indicated thermal efficiency was mainly affected by compression ratio and fuel film of the wall of combustion chamber. Emission of NOx and smoke were affected by the amount of pre-mixed combustion and injection through. The static fuel supply timing was increased to 18oCA BTDC, which leads to 0.21 BSU smoke emission at the operating point of rate power and maximum torque.