Abstract: A method was developed to determine the concentration of activated species in strong ionized discharging plasma,which could be used to measure the apparent oxidation ability.In the experiments,the excess ferrous ions reacted with the activated species in plasma,and then the remained ferrous ions was titrated with potassium permanganate,the amount of which was used to determine the concentration of the activated species.Some influencing factors,such as pH value,flow of discharging gas,discharging power,pressure of discharging gas and reaction time,were evaluated,respectively.The results of experiments show that pH=6.0 was the proper initial pH value;the reaction time had less effect on the determination,so 3 minutes was suitable;the concentration of the activated species increased with the increases of discharging power and the pressure of discharging gas,but decreased with the increase of the flow of discharging gas.It has shown that the reproducibility and the sensitivity of the determination method are all satisfied,and the detection limit reaches 3.91×10^-5 mol/L.