Abstract: The impacts of meteorological fields simulated by MM5 and WRF models on air quality forecasting by the CMAQ model are explored. Emphasis is placed on comparing the inverse effect of SO₂ and NO₂ sources by adaptive Nudging scheme and the twomodels in North China, the difference of their forecasting concentrations,and on analysis of physical mechanism of improved simulation of planet boundary layer (PBL) height and relative humidity. The results indicate that diurnal variation and vertical profile of four meteorological elements simulated by the WRF model are in better agreement with MICAPS observations than those by the MM5 model. The relative humidity and the PBL height simulated by the MM5 model are far from the observed values, but those simulated by WRF model are closerto the observations. The relative humidity and PBL height are key factors in the forecasting of SO₂ and NO₂ mass concentrations with the CMAQ model. The variation of these factors significantly influences the forecasting of SO₂ and NO₂ mass concentrations. Therefore, improved simulation of PBL height and relative humidity has positive impacts on SO₂ and NO₂ mass concentration forecasting accuracy. The main reason for smaller simulative error of SO₂ mass concentration is less contribution of vertical transportation and mass adjusting process to SO₂ mass concentration; the main reason for smaller simulative error of NO₂ mass concentration is less contribution of chemical reactive process to NO₂ mass conentration.