A three-dimension computational fluid dynamics study on spray tower of aqueous ammonia process is presented. The gas flow is described using standard turbulence model ,and the motion of the liquid droples is described in a Lagrangian way, using the stochastic discrete particle mode. The influence of parameters including ammonia concentration, liquid gas ratio and porosity of air distributor on the efficiency of FGD was studied. When liquid-gas ratio is about 2.2, the concentration of NH3 is about 0.09% and the porosity of air distributor is between 70% and 80%, the SO2 removal efficiency of spray tower will be higher from the result. It can be taken as a reference for process design, optimization and intensive study of desulfurization by aqueous ammonia process.