A 3-D chemical transport model (OSLO CTM2) is used to investigate the impact of the increase of NOx emission over China.The model is capable to reproduce basically the seasonal variation of surface NOx and ozone over eastern China.NOx emission data and observations reveal that NOx over easternChina increases quite quickly with the economic development of China.Model results indicate that NOxconcentration over eastern China increasingly rises with the increase of NOx emission over China,and accelerates to increase in winter.When the NOx emission increases from 1995 to its double,the ratio of NO2/NOx abruptly drops in winter over northern China.Ozone at the surface decreases in winter with the continual enhancement of the NOx level over eastern China,but increases over southern China in summertime.It is noticeable that peak ozone over northern China increases in summer although mean ozone changes little.In summer,ozone increases in the free troposphere dominantly below 500 hPa.Moreover,the increases of total ozone over eastern China are proportional to the increases of NOx emission.In a word,the model results suggest that the relationship between NOx and ozone at the surface would change with NOx increase.