Abstract: Fine particles and SO₃ acid mist from the inlet and the outlet of the wet flue gas desulfurization（WFGD） systems in two coal-fired power plants were measured and the effects of different technologies and coal qualities on the removal of fine particles and SO₃ acid mist were investigated. The results show that the removal efficiencies of fine particles and SO₃ acid mist in the double-tower system are obviously higher than those in the single-tower system. The size distributions of fine particles at the inlet of WFGD systems are similar. They shift to the smaller end after desulfurization with higher proportion of PM_2.5, which is more obvious in the double-tower system. Particles in the flue gas are removed by the WFGD system, while new fine particles are formed during desulfurization, which are mainly calcium sulfate with clintheriform and prismatic shape. The removal efficiencies of the double-tower system and the single-tower system on SO₃ acid mist are 30%~40% and 50%~65%, respectively. With the increase of the inlet concentrations of SO₃ and particles, the removal efficiencies increase and the blue plume occurs with the high-sulfur coal.