Abstract: A new correction method was proposed for catalyst activity of SCR denitrification system in large power plant boilers. The specific way is to correct the measured data of catalyst activity obtained in laboratory with field test results, which can reflect the real denitrification capability of the SCR reactor. Results show that the method proposed may serve as a new technical means in evaluation of catalyst renewal schemes, since it has a high accuracy in performance calculation of both the catalyst and the SCR reactor, and it is able to reflect the real activity of the catalyst used.