To evaluate the changes in ammonia escape rate of selective catalytic reaction (SCR) denitrification devices caused by frequent peak shaving of coal-fired power units under large-scale grid connection of new energy. A three-dimensional numerical model of SCR denitrification was constructed using MATLAB programming method, and the influence of catalyst structural parameters on denitrification performance was studied. The results show that the catalyst pore pitch has a significant impact on the denitrification efficiency and ammonia escape rate. At a reaction temperature of 629.15 K, the catalyst pore pitch increases from 6 mm to 12 mm, the SCR denitrification efficiency decreases from 72.63% to 51.04%, and the ammonia escape rate increases from 9.76% to 25.1%. The denitrification performance of SCR increases with the increase of catalyst length. At a reaction temperature of 639.15 K, the catalyst length increases from 300 mm to 1 000 mm, and the denitrification efficiency increases from 36.23% to 69.05%. The ammonia escape rate decreases from 51.15% to 8.90%. The decrease in power plant load is beneficial for the reduction of ammonia escape rate. The denitrification efficiency increases from 67.71% to 73.28% when the load decreases from 550 MW to 330 MW, and the ammonia escape rate decreases from 1.1% to 0.14%. The deterioration of coal quality leads to an increase in ammonia escape rate. The calorific value of coal decreases from 16747.2 J to 15491.16 J, and the denitrification efficiency increases from 71.14% to 71.73%. The ammonia escape rate increases from 1.47% to 1.72%.