Abstract: A PM_2.5 agglomeration technique was developed to control PM_2.5 emission and treat desulfurized wastewater. The removal of PM_2.5 by electrostatic precipitator (ESP) with evaporation of desulfurized wastewater was investigated experimentally based on a coal-fired thermal system. Effects of wastewater evaporation on fly ash, electric performance were analyzed, and chemical agglomerants and nozzle diameter were considered as two affecting factors. The results show that the average particle diameter increases from 0.15 to 1.0 μm after evaporating desulfurized wastewater. The PM_2.5 concentration at ESP outlet decreases by more than 10% under typical conditions. With the addition of agglomerants, PM_2.5 concentration at ESP outlet decreases by more than 25%. Raising temperature, reducing nozzle diameter and increasing chemical agglomerant amount have a positive effect on PM_2.5 removal.