Integration of coal-fired power plants with NH3-based CO2 capture is a promising technology for CO2 capture. However, the output and efficiency of the original coal-fired power plant are reduced because the integration requires energy. This work studied three typical coal-fired power plants with the capacities of 330, 660, and 1000 MW and turbine levels of N330-16.67/538/538, N660-24.2/566/566, and N1000-25/600/600, respectively. The integration of these coal-fired power plants with the same NH3-based postcombustion CO2 capture system was established. Heat consumption, energy penalty, and other evaluation indicators were obtained through an Ebsilon simulation. Among the three coal-fired power plants, the thermal efficiency of 1000 MW is the highest, whereas that of 330 MW is the lowest. The energy penalty of the 660 MW coal-fired power plant is the highest, whereas that of 330 MW is the lowest. To fully analyze the integration performance of power plants with different capacities, comprehensive evaluation of the gray correlation of an integrated system from six aspects based on the gray relational degree method is carried out. Analysis results show that the correlation coefficient of the 1000 MW coal-fired power plant is the highest, whereas that of 330 MW is the lowest. The energy consumption formula that was once proposed for a 660 MW coal-fired power plant is further optimized, and a new evaluation system of an integrated system combining an energy consumption formula and a gray correlation coefficient is presented.