On-road emission tests were conducted for six low-speed vehicles using SEMTECH-DS, a Portable Emission Measurement System (PEMS). The instantaneous speed and emission concentration data of CO₂, CO, NO_x and HC were collected, and the relationship between the driving cycle and emission, and the emission factors are analyzed based on the testing data. The results show that the emission factors of CO₂, CO, NO_x and HC decrease with the increase of speed and increase with the increase of acceleration; the emission rates are the highest in the acceleration mode, followed by the cruising mode, and are the lowest in the idling mode. The emission rates of the four pollutants for low-speed vehicles have a very good correlation with VSP; the average emission factors of the CO₂, CO, NO_x and HC for tested low-speed vehicles are 110.1, 1.66, 1.78 and 0.49g·km^-1, respectively. The CO emission factors are comparable to the regulated values of light-duty diesel trucks with Nation II technology; and NO_x and HC emission factors are comparable to the regulated values of light-duty diesel trucks with Nation I technology.