Based on the rate-based process simulation, performances of MEA and NH3 based large-scale CO2 capture in packed columns under different flue gas parameters were investigated. Simulation results show that the CO2 regeneration energy for the MEA based process is lower than that for the NH3 based process, which is mainly because the flow rate of the MEA solution is significantly lower than that of the aqueous ammonia. The MEA leakage concentration is far lower than the NH3 leakage concentration, and this indicates that the NH3 abatement system should be added for dealing with the NH3 slip in the NH3 based CO2 capture process. With the flow rate of the flue gas increasing, the liquid gas ratios for both processes decrease, which gives rise to the decrease of the CO2 removal efficiencies for the two processes. Since the liquid gas ratios are very high, the temperature of the flue gas has little effects on the MEA and NH3 based CO2 capture processes. The comparative studies on the effects of the flue gas parameters can provide technical guidance for the pretreatment of the flue gas before CO2 capture.