Abstract: In order to exploring the influence of EGR on combustion and emission characteristics in a low load working condition on a light-duty diesel engine. Taking one high pressure common rail light-duty diesel engine as the research object, a visualization platform for cylinder working process of a diesel engine was built. Influence of EGR on combustion process and emission characteristics was studied through cylinder combustion process high-speed photography, cylinder pressure and heat release rate. The study illustrated that spray and combustion process was analyzed directly through visualization platform. In a condition of low load, with the EGR rate increased (≤30%), the ignition delay shortened, and the combustion process extended, meanwhile the maximum combustion pressure, the peak of heat release rate and the average temperature of combustion last stage rose. Compared with the EGR rate of 10%, the NOX , HC and CO emissions reduced by 65.6%, 46.4% and 28.7%, soot emissions first decreases and then increases. The soot emission and fuel economy worsened when the EGR rate was over 30%. This study provided an effective way of reducing diesel emission