An engine system for controlling flow of exhaust gas may include an intake line to receive external air, an engine including a combustion chamber to combust the external air and a fuel supplied through the intake line, to generate driving torque, an exhaust line to exhaust the exhaust gas combusted in the combustion chamber of the engine, a turbocharger including a turbine operated according to exhaust gas flowing through the exhaust line and a compressor to compress the external air flowing through the intake line, a catalyst device to reduce a harmful component included in the exhaust gas passing through the turbine of the turbocharger, a bypass line branched from the exhaust line between the combustion chamber and the turbine and converged in the intake line between the compressor and the combustion chamber, and a bypass valve disposed in the bypass line to selectively open/close the bypass line.