Converter gas must be purified by the wet electrostatic precipitator for the combined cycle power plant because of its high dust concentration. However, most of the electrostatic precipitator is placed after the gas tank in order to operate safely. This will result in larger amounts of dust entering into the gas tank or the atmosphere. It causes the gas tank's seal damaged and air pollution. Based on the above reasons, the authors put forward a new process which places the wet electrostatic precipitator before the gas tank for purifying the converter gas, and analyzed the feasibility of this process. The research on corona discharge of converter gas in electrostatic precipitator, V-I characteristics affected by the water pressure and collection efficiency of the dust particles was carried out at an experimental system. The results show that corona discharge performance of converter gas was good and the V-I characteristic curve gradually moves down when the gas pressure increases. Spraying water can promote the collection efficiency of the dust particles. When the water pressure is 0.3MPa, the collection efficiency is 97.4%. The optimal water pressure in wet electrostatic is 0.3~0.5 MPa. From the results and analysis, it is feasible to purify converter gas by using the wet ESP which is placed before the gas tank.