Abstract: By using the method of Discharge Flow-Resonance Fluorescence, the reaction of OH+SO_2+M was studied. The effect of wall reacton, diffusion and side reaction on the rate constants of the reaction was discussed. In the atmosphere of Ar or N_2, at 298K, the measured rate constants of the reaction were (1.5+0.32) × 10~(-31) cm~6 molec~(-2) s~(-1) and (3.6±0.79)×10~(-31)cm~6 melec~(-2) s~(-1), respectively.