The invention discloses a control method applied on a power converter, and an operating method thereof. The control circuit comprises a multifunctional pin, a zero-crossing signal generator and an overvoltage detector. The multifunctional pin is used for receiving an auxiliary current which is generated by an auxiliary winding of the power converter and an input current. The zero-crossing signal generator is used for generating a zero-crossing signal according to the auxiliary current. The overvoltage detector is used for generating an overvoltage signal according to the auxiliary current. The control circuit generates a switch control signal of the power switch to the power switch according to the zero-crossing signal, or generates an overvoltage protecting signal to the power switch according to the overvoltage signal. Therefore the control circuit can simultaneously realize functions of low-voltage protection, over-temperature protection and overvoltage protection on an existing six-pin integrated circuit or high-voltage eight-pin series integrated circuits.