In this study, several methods are proposed to improve the denitrification (De-NOx) performance of the selective catalytic reduction (SCR) system. To illustrate how the proposed methods can be applied, the numerical analysis for the SCR system of an industrial-scale thermal power plant is conducted. There are two important indices affecting the performance of SCR system: one is the degree of mixing of the injected NH3 and the other is the uniformity of flow velocity before entering the catalyst layer. To improve the NH3 mixing, a static mixer in a location downstream of the ammonia injection grid (AIG) is generally installed. However, the uniformity of flow velocity distribution is severely aggravated as the mixer induces vortex. Therefore, it is suggested to place the mixer away from the catalyst layer to enhance the NH3 mixing and the uniformity of flow velocity together. The effect of the number of injection nozzles of the AIG on the SCR performance is also investigated. The number of nozzles of the ammonia injection grid can be reduced without affecting the uniformity in flow velocity. However, too much reducing the number of nozzles would result in improper ammonia mixing. Therefore, it is recommended to reduce the number of nozzles within a tolerable range of the NH3 mixing. (C) 2020 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.