A cylinder inflow exhaust gas amount calculation system of an internal combustion engine is provided with an intake passage, an exhaust passage, an exhaust gas recirculation passage connecting the intake passage and exhaust passage, and an exhaust gas flow rate control valve arranged in the exhaust gas recirculation passage for controlling the flow rate of the exhaust gas flowing in the exhaust gas recirculation passage, the system calculating an amount of passage exhaust gas defined as an amount of exhaust gas passing through an exhaust gas flow rate control valve, utilizing a parameter changing said amount of passage exhaust gas and the system calculating an amount of cylinder inflow exhaust gas defined as an amount of exhaust gas flowing into a cylinder, utilizing said calculated amount of passage exhaust gas.