A method of controlling a sleep maintenance motion includes: determining, by a sleep maintenance mode entry determiner, whether a vehicle enters a sleep maintenance mode; when the vehicle enters the sleep maintenance mode, calculating, by an engine target speed profile calculator, an engine target speed profile; calculating, by an engine/hybrid starter generator (HSG) target torque calculator, an engine/HSG target torque based on the calculated engine target speed profile; and controlling, by the sleep maintenance mode entry determiner, a sleep maintenance motion based on an operation of an engine/HSG.