Abstract: Baskward trajectory cluster analysis is used to determine the source regions and variation of surface SO2 at Lin’an regional background station under different weather conditions in Sep. and Oct. 1994. Furthermore, by using Lagrangian transport, dispersion and deposition model, the contributions from different areas to surface SO2 concentrations at Lin’an station are calculated. In comparison with the observations, it is shown that the model could be well to simulate the variations of surface SO2 at Lin’an. Meanwhile, it is also shown that the concentrations and variations of surface SO2 observed at Lin’an station could reflect those of eastern China.