The separation of fine particles from coal-fired flue gas by chemical and physical reactions was investigated experimentally in a wet flue gas desulfurization (WFGD) system using a cascade of double-towers system. The flue gas particles were collected by the Andersen 8-stage impactor. The mass concentration and particle size distribution of flue gas particles were investigated in this paper. Base on the analysis of the scanning electron microscopy/energy dispersive X-ray spectrometry (SEM-EDX), X-ray diffraction (XRD) and inductive coupled plasma-atomic emission spectrometery (ICP-AES), the morphological characteristics, major and minor-element concentrations of particles were studied. The results indicate that the size distribution of fly ash particles at the inlet of the WFGD system was typically distributed bimodally. After the desulfurization, although a bimodal distribution was still observed, all peak positions displaced to the smaller. Furthermore, the contents of S and Ca also increased. Fine particles in the flue gas consist of about 26.48% limestone and 41.19% gypsum particulate matters, eventually forming the Ca11.3Al14O32.3 crystal. The net removal efficiencies of double tower WFGD system reached 84.16 % for the original particles, which was similar with the conventional single tower WFGD system. The entrainment of recirculated slurry contributed to the submicron particles emissions, and the total removal efficiency of the double towers WFGD system was reduced to 51.1%.