The disclosure provides a power conversion circuit with a multi-function pin and a multi-function setting method thereof. The multi-function pin is coupled to an external setting circuit. The power conversion circuit includes a first function circuit, a second function circuit, and a judging circuit. The first function circuit is coupled to the multi-function pin. The second function circuit is coupled to the multi-function pin. The judging circuit is coupled to the multi-function pin, the first function circuit, and the second function circuit. The judging circuit provides a setting current to the multi-function pin, so that the external setting circuit generates a voltage according to the setting current. The judging circuit judges the type of external setting circuit according to voltage so as to activate the first function circuit or the second function circuit accordingly. The disclosure also provides a multi-function setting method in which the power conversion circuit automatically activates the corresponding function according to the type of external setting circuit.