This paper researched on vehicles’ emissions in Nanjing based on IVE model and presented the method to quantify the main inputting parameters of IVE model. This research has collected the traffic of different types of roads in Nanjing. The light-duty vehicles, taxis, buses and trucks respectively accounted for 73.4%, 13.3%, 10.3% and 3.0% of the total traffic volume. According to vehicle driving condition data collected by GPS, the driving cycle of light-duty vehicles in Nanjing was defined. The on-road vehicles’ emission data were measured using the on-board vehicle emission analyzer made by ourselves. Then the correction factors of NOx in IVE model could be obtained using the testing emission data. The results of IVE model showed that the daily NOx emission of light-duty vehicles, taxis, buses and trucks in Nanjing city were 17.79t, 5.51t, 146.37t and 83.78t. Buses and trucks were the main emission sources of NOx, with the contribution of 57.75% and 33.06%.