A mathematical model of droplet motion and evaporation in flue gas has been established to analysis the feasibility of desulfurization wastewater evaporation treatment in flue gas duct. The parameters such as the duct structure， the flue gas temperature and the diameter liquid droplet are analyzed; the states of evaporation of liquid droplets are obtained under various working conditions. Moreover， a further comprehensive optimization and quantitative analysis have been carried out on unevaporated liquid quantity with various flue gas temperature and droplet diameters. The results show that this approach of evaporating desulfurization wastewater by flue gas in duct is feasible. The study provides support in further practical application for engineering.