Disclosed herein is a method and system for charging a battery of a hybrid electric vehicle driven with power of an engine and/or a motor, the method including detecting an accelerator pedal position by an accelerator position detector, detecting a brake pedal position by a brake position detector, determining, by a controller, when the vehicle is coasting based on manipulation of the accelerator pedal and the brake pedal; determining when a state of charge of the battery is a charged state having a value equal to or smaller than a set value; and maintaining the engine in a driving state and rotating the driving motor with engine power to charge the battery with generated power of the driving motor when the state of charge of the battery is the charged state having the value equal to or smaller than the set value and the hybrid electric vehicle is coasting.