Abstract: In order to investigate the emission levels of heavy duty diesel vehicles in China and to determine emission factors for CO, HC, NO_x, PM, and other pollutants, heavy duty diesel vehicles meeting the China Stage Ⅲ emission standard were investigated under different loads (0%, 50%, 100% and 120%) and two running cycles with a great difference on the driving characteristics. Both Portable Emissions Measurement System (SEMTECH-DS equipment for gaseous pollutants and DMM instrument for PM measurement) testing and complete heavy-duty vehicle chassis dynamometer testing (as required in the emissions regulations) were conducted in this study. The results showed that vehicle loads significantly effected on the vehicle emission factor measurements. Emission factors of NO_x, PM tested under 120% load could be nearly 90% higher than that when tested under 0% load. The emission factors tested with the driving cycle of the low average speed and long idle time could be about 30% higher than that when tested with a high average speed and short idle time driving cycle. Gaseous pollutant emissions measurements showed a significant correlation between the SEMTECH equipment and the CVS system on the chassis dynamometer. However, the variation of PM results were more than 50% between the DMM instrument and the CVS system on the chassis dynamometer.