Abstract: Based on the regional acid deposition model (RADM), a high resolution model (EM3) for species ezchaage within the troposphere (TL) is dasigaed, EM3 differs considerably in the following 5 aspects from RADM, First, the vertical grid levels in planetary boundary layer (PBL) are increased. Second,layering vertical eddy diffesivity patterns within TL are considered, Thrid, layering horizontal eddy diffusivity patterns within TL are used. Fourth, new dry deposition velocity pattern including the effect of plant canopy layer vertical structure is adopted.Fifth,advective schemes of secondorder moment consei vation with less numerical diffusion is used.OSCAR IY case is comparatively simulated with both EM3 and RADM. The results show that 3-D mass distribution laws whole TL are forecasted by EM3 better than RADM, Under the same conditions,all ratios of the center concentration simulated with both models in lower PBL are more than 1.8. the maximum can be more than 3.