OH radical in the corona discharge with pipe-nozzle-plate electrode has been diagnosed by optical emission spectroscopy. Spatial variations of OH radical emission in discharge gap have been measured Relative intensity of OH radical emission spectroscopy increases with increasing water vapor flux injected into the reactor or intensity of electric field supported. In positive pulsed corona discharge, relative intensity is higher than that in positive DC corona discharge and lower than that in negative DC corona discharge. Strongest intensity of OH radical spectrum appears within the range of 5 nun near the discharge nozzle-electrode. In addition, it is proved that the efficiency of desulphurization from flue gas by pulsed corona discharge plasma processes can be improved when OH radical is produced in the reactor