A charger, including a power conversion circuit, a charging interface, and an overcurrent protection circuit, where the charging interface includes a power cable, a ground cable, a signal cable, a resistor and a switch device, where a first end of the resistor is connected to the power cable, a second end of the resistor is connected to the signal cable, in a process in which the charger charges a terminal device and when a difference between a voltage of a first end of the switch device and a voltage of a second end of the switch device is greater than or equal to a first voltage threshold, the second end and a third end of the switch device are connected such that the power cable and the ground cable are connected to generate an overcurrent, and the overcurrent protection circuit controls the power conversion circuit to stop current output.