A method of calculating an exhaust gas recirculation (EGR) rate using combustion pressure of a cylinder of an internal combustion engine includes: detecting, by a pressure sensor, the combustion pressure of the cylinder in real time; calculating, by a processor, a data characteristic of a combustion pressure waveform per cycle through principal component analysis based on the detected combustion pressure of the cylinder; calculating, by the processor, a moment of the combustion pressure waveform per cycle by calculating a probability distribution based on the detected combustion pressure of the cylinder; calculating, by the processor, the EGR rate using the calculated data characteristic, the calculated moment, and engine operating conditions; and controlling, by the processor, the EGR rate based on the calculated EGR rate and a target EGR rate.