The emissions from 7 urban freights were tested using a portable emission measurement system (PEMS) and analyzed based on the vehicle-specific power (VSP) method. The results show that both gaseous pollutants and PM emissions increase with VSP. With regard to CO and HC, emissions decrease with elevated speed and acceleration. The PM and NOx emitted from China IV vehicles are significantly less than those from China III vehicles, but emissions of CO and HC exhibit a different tendency, thus necessitating further research. In addition, speed and acceleration show a slight influence on NOx emissions. The VSP plays an important role in the emissions from urban freight trucks. Therefore, a comprehensive evaluation of the emission characteristics of these vehicles in megacities is needed in order to take effective measures.