The real driving emissions of a lightduty diesel vehicle at plateau areas of 1 900 m, 2 200 m, 2 400 m and 3 000 m in Qinghai province were tested and the collected data were processed with the moving average window method to form the emission data. The vehicle emission results were evaluated and the effects of altitude on emissions were analyzed. The results indicate that the CO and PN emissions first increase and then decrease with the increase of altitude and reach the peak at 2 400 m. However, NOx emissions first decrease and then increase and reach the minimum at 2 400 m. In addition, CO and PN emissions and NOx emissions in four areas are lower and higher than the regulated limits respectively and the conformity factors are 7.44, 7.11, 6.44 and 8.