An engine system may include an intake line, and a cylinder deactivation (CDA) device selectively deactivating a portion of combustion chambers in the engine. The engine system may further include a first exhaust manifold connected to a first plurality of combustion chambers mounted with the CDA device, a second exhaust manifold connected to a second plurality of combustion chambers without the CDA device, a first exhaust line connected to the first exhaust manifold, a second exhaust line connected to the second exhaust manifold, and a third exhaust line connected with the first and second exhaust lines through an exhaust gas processing device. In addition, a turbocharger including a turbine is mounted at the first exhaust line and rotated by exhaust gas. An air injection device may supply air to the second exhaust manifold or the second exhaust line in a catalyst heating mode of the exhaust gas processing device.