In recent years, air pollution has become one of the important factors limiting the improvement of urban living environment quality in Xi'an City, China. The local government has taken a series of measures to control air pollution, among which the motor vehicle restriction policy is most favored due to its strong feasibility, less public investment and simple operation. Based on the analysis of the trend of air quality changes in Xi'an from 2016 to 2020, R language is used to establish a generalized additive model for the relationship between relevant influencing factors (motor vehicle restriction policy, average wind speed, relative humidity and average temperature) and air quality, and then fitting analysis and correlation test are carried out. The results show that there is a significant correlation between vehicle restriction policy and air quality improvement in Xi'an City.