An apparatus for controlling power generation of a vehicle includes an alternator for generating electricity using an engine torque. A controller is configured to calculate a difference between a first duty value and a second duty value and to transmit a control signal based on the difference. The first duty value is an output duty value of the alternator before reaching a predetermined time, and the second duty value is a current output duty value of the alternator. A regulator gradually increases the amount of power generated by the alternator during a delay time based on the control signal received from the controller.