A buck switching regulator includes: a power stage, which includes: an upper-gate switch, a lower-gate switch and an inductor, connected with one another at a switching node; and a supply control switch, controlling the power supply form an output terminal to a load. An overvoltage protection method includes the following steps: (A) sensing a voltage of the switching node, to obtain a switching node voltage; (B) determining whether an overvoltage event occurs in the switching node voltage; and (C) if it is determined yes in the step (B), outputting a protection signal. An overvoltage event is determined directly according to the switching node voltage, not directly according to the output voltage.