It is the purpose of this paper to investigate the nature of ionic wind (IW) in corona discharging field for the model electrostatic precipitator (EP). On the basis of the results about IW velocity measured by a Thermistor-anemometer, ion density and the efficiency of IW were calculated. These calculated results were small values unexpectedly. Ion velocity by trial calculation was larger than IW velocity and IW velocity distribution at the place of plate electrode was such as characterised by normal functions. Moreover, it is an important problem for EP that the charging particle velocity due to Colomb force from trial calculation is smaller than the IW velocity.