A multi-level buck converter includes an input power source, an input capacitor, first to fourth switches, a clamp capacitor, an output inductor, a clamp switch, a clamp diode, an output capacitor, an output load, a current detection circuit, a voltage detection circuit and a control circuit. The current detection circuit detects whether an inductor current of the output inductor exceeds a predetermined current value, and if so, the output clamp signal controls the clamp switch to be turned on. The voltage detection circuit generates a duty cycle control signal according to an error between an output voltage and a target output voltage. The control circuit controls the first to the fourth switches to sequentially enter a first mode, a second mode, a third mode, and a fourth mode in a first part of a duty cycle.