This paper introduced a new combustion system of the compression-ignition CNG engine, which was developed by the authors. The low heat rejection separate combustion chamber and compound gas injection system were employed in the new combustion system. The assistant heating temperature, the ceramic coating of combustion chamber, the intake air heating temperature and the effect of EGR on combustion and emission were studied. The results showed that heating temperature of the ceramic glow plug, the intake air and divided chamber geometry all had obvious influence on combustion and emission. The CNG engine could be started at the ordinary temperature just with the ceramic glow plug. The appropriate ratio of EGR could reduce HC and NOx exhaust, and could keep the combustion process of the CNG engine stabilization.