Abstract: As for the main reaction mechanism in desulfurization of flue gas by pulsed corna or electron beam,which generates low temperature plasmas,there were two presumptions:gas phase reactions and heterogeneous reactions.The results of this work indicate that with an appropriate partial pressure of water vapor,there exists liquid layers on the inner surfaces of the reactor and the solid deposits.The radicals of SO3 play an important role in the chain processes of oxidizing sulfite ons to sulfate ions.By solving the kinetic equations,it can be found that the hydroxyls absorbed by the liquid phase contribute over 80％ percent of desulfurization rate,which is over ten times of that due to gas phase reactions.It suggests that the main mechanism is the plasma-activated liquid phase reactions.The calculated results not only agrde with the experiment but also predict the effect of effective area factor.The prediction is proved by the experiments.