Abstract: The mechanism of the distributions of tropospherico zone and its precursors over China has been simulated by means of three-dimensional MM5 and chemical model in summer and winter time, 16～18 August 1994 and 7～9 January 1995, and the distribution of ozone over Tibetan Plateau in summer time is deeply discussed. The simulated results indicated that the distributions of surface ozone and NOx have a good agreement with measured results, and human activities and photo chemical reactions are the main factors controlling the surface ozone and NOx concentration. In addition, higher ozone concentrations are coincided with the air convergence, and the lower are related to the air divergence. In summer, over Tibetan Plateau the strong flow convergence results in higher ozone concent rations in the lower troposphere; and the strong flow divergence results in lower ozone concent rations in the upper troposphere. In winter time ozone concentrations show large scale characteristics controlled by western flow, the ozone concent rations in jet area are lower than the other areas.