Particulate matter (PM) emission of non-road diesel engines is more and more stringently restricted by US, EU, Japan, etc. In order to achieve these emission regulations, diesel particulate filter (DPF) system is applied. However DPF system requires extra fuel consumption in order to burn accumulated particles. Furthermore, since it is difficult to install large DPF systems in limited packaging space of non-road applications, compact DPF system is desirable.Reducing soot emission with engine technology is effective for reducing PM emission, which results in reducing extra fuel consumption and downsizing or removing of DPF system. Soot emission level mainly depends on excess air ratio (EAR), and can be reduced by keeping EAR high (lean combustion). However, lean combustion under the limited amount of air and maximum in-cylinder pressure requires decrease in fuel injection quantity, and yields decrease in engine power. Therefore, in order to achieve low soot emission without decreasing engine output, low soot combustion with minimum EAR without a significant increase in soot emissions is required. Furthermore, low compression ratio is thought to be one method for increasing power density under the limited maximum in-cylinder pressure.In this study, the effect of compression ratio on soot emission is investigated under the constant EAR assuming higher load engine operating condition.The results show that soot emission gets lower as compression ratio is lower because of the increase in volume of combustion chamber. In addition, the effects of fraction of premixed combustion or injection duration on soot emission are also discussed.