To understand the observed characteristics of transboundary air pollutants transport over the East Asia, an atmospheric transport model which includes detailed chemical reactions, the STEM (Carmichael et al, [3]), was applied. It was found that wind pattern variations associated with a synoptic scale pressure system are extremely important for the transport of pollutants in this region. An on-line transport model coupled with Regional Atmospheric Modeling System (RAMS, Pielke et al., [9]) are also applied during the rainy season (June). On-line transport model explained well the sulfate concentration variation, and indicates that the strong concentration gradients exists at the northern side of rainy meso-front (typically at Korea and Kyushu Japan). It was found that the location of rainy meso-front plays an important role for sulfate concentration level in Japan and Korea.