The present disclosure discloses a system and method of adjusting an output parameter of a secondary battery. The system according to the present disclosure determines a voltage, a current, and a temperature of the secondary battery, determines a state of charge of the secondary battery using the current, determines a deration target current value calculated from a maximum value of a predefined resistance change rate, which corresponds to the state of charge and the temperature, and an output maintaining time, when the voltage of the secondary battery decreases to a preset threshold voltage or lower, and provides an output parameter including at least one of the deration target current value and a deration target output value determined therefrom to a control system of a load device supplied with power from the secondary battery.