In the context of the promotion of ultra-low emissions in the iron and steel industry, the technology of embedded SCR and SNCR coupled denitrification has been popularized and applied in pellets gas treatment due to its high denitrification efficiency and high cost performance. The reasons for the increase of NO_x mass concentration are systematically analyzed and corresponding solutions are proposed in view of the situation that the NO_x mass concentration increases again through the preheating section after the embedded SCR denitrification device is installed in a certain engineering project. The results show that the increase of NO_x mass concentration after SCR denitrification is not caused by gas leakage or air mixing, but by the thermal decomposition process of Brazilian coarse powder in the pellets component and the nitric acid cleaning solution mixed in it during the drying and preheating process, which accounts for 28.7% and 58.9%, respectively. Through the temperature-programmed test of the material, it is found that there are two peak NO_x emission peaks belonging to different sources near 460 °C and 650 °C, which are close to the temperature of the two gases at 370 °C in the drying II section and 650 °C in the preheating I section, resulting in the rapid release of NO_x near the temperature of the two windows. However, the embedded SCR denitrification technology is an efficient denitrification process developed based on making full use of the waste heat in each temperature range, so it is difficult to reduce the NO_x emission by adjusting the temperature range of each section of the grate. Based on this, the optimization measures of replacing the nitric acid cleaning solution of the filter are proposed, so that the NO_x emission can be significantly reduced, and the pellets gas can meet the ultra-low emission standard.