A DC-DC controller and a control method thereof are provided. The DC-DC controller is coupled to an output stage. The output stage receives an input voltage and provides an output voltage. The DC-DC controller includes a transient boost circuit, a ramp oscillator, a combination logic circuit, a first comparator and a pulse width modulation (PWM) generator. The transient boost circuit generates an adjusting signal according to a variation of the output voltage. The combination logic circuit controls the ramp oscillator to generate a ramp signal according to the adjusting signal. The first comparator generates a first signal according to the ramp signal and an outputted feedback voltage related to the output voltage. The PWM generator generates a PWM signal according to the first signal, so as to control the operations of the output stage.