The present invention provides an interface circuit, wherein the interface circuit includes a switching circuit, an over-voltage detection circuit and a control signal generating circuit. In the operations of the interface circuit, the switching circuit is configured to receive an input signal from an input terminal, and selectively transmit the input signal to an internal circuit. The over-voltage detection circuit is configured to detect whether a voltage level of the input signal is greater than a threshold value, and accordingly generate at least one over-voltage signal. The control signal generating circuit is configured to generate a control signal according to said at least one over-voltage signal, to control the switching circuit to be in one of three or more states.