Daily running mileage and running time of the taxi is long so its pollutant emission is an important source of road traffic pollutant emission. This paper analyzes and studies the pollutant emissions of Xi'an in different periods of a day built on the driving data of 370 taxis on a definite working day in 2014. The paper calculated the VSP value according to the taxi GPS data and divided the VSP by the interval unit 1kW/ton to get the VSP distribution. We judge the traffic status of this period by examining the characteristics of taxi speed in different periods of the day. The localization parameters and VSP distribution are substituted into the MOVES model to estimate the emissions of CO, CO2, HC, and NOX in discrete periods, and the total emissions of taxi pollutants in Xi'an in 2014. The results indicate that: 1) taxi speed is mainly concentrated in the 20-45km/h, of which 30-40km/h accounts for the highest proportion. 2) The high emission of taxis is taken from 7:00 to 20:00. The emissions of CO, CO2, HC and NOx were 8.6%, 7.8%, 11.1% and 8.8%, 7.14% and 7.14%, 12.3% and 10.7%, respectively. 3) in 2014, the total emissions of CO, CO2, HC and NOx of motor vehicles in Xi'an were 415.74, 179.36, 428.97 and 28.92t respectively.

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