Abstract: To analyze on-road emission characteristics of Beijing taxies, on-road taxi emission test was conducted using sensor emission technology (SEMTECH-DS). The relationships between driving characters of speed, acceleration, vehicle specific power (VSP) and the emissions of CO, HC, NOx, CO₂ were analyzed based on the test data, respectively. The results show that, with the increase in taxi speed, the emission rates of CO, HC, NOx respectively increase first and then decrease, but CO₂ emission rate increases without decreases. In different ranges of speed, all kinds of pollutant emission factors and emission rates increase with the increase in taxi acceleration. Moreover, all kinds of pollutant emission factors and emission rates increase with the increase in VSP and they are correlated with VSP index positively. It seems reasonable to quantify taxi emissions using the index of VSP intervals.