A wet electrostatic precipitator (ESP) is disclosed to have a housing, several discharge wires, two roughened collection electrodes coated with TiO2 or SiO2 nanoparticles, two porous metallic plates, and two roughened glass plates coated with TiO2 or SiO2 nanoparticles. The porous metallic plates and the glass plates coated with TiO2 or SiO2 nanoparticles located above the collection electrodes are used to enhance the uniformity of the water film. When particles are introduced into the ESP, they are charged by gas ions generated by corona discharge, and then migrate to collection electrodes due to electrostatic force. Finally, particles are removed by uniform water film flowing downward along the collection electrodes. Furthermore, pulse jet passing through the small holes on the collection plates is used to clean discharge wires, maintaining electric corona strength and prolonging the operation life.