An insulation impedance detection circuit for an on-board charger, comprising a voltage division circuit, a biasing circuit, an impedance matching circuit, a voltage sampling circuit and a controller, wherein, terminals of the voltage division circuit are electrically connectable to a first AC terminal and a second AC terminal of the on-board charger respectively, and are electrically connected selectively to a first terminal of the impedance matching circuit; a second terminal of the impedance matching circuit is electrically connected to a first terminal of the biasing circuit, a second terminal of the biasing circuit is grounded, and a third terminal of the impedance matching circuit is electrically connected to an input terminal of the voltage sampling circuit; an output terminal of the voltage sampling circuit is electrically connected to the controller for outputting an insulation impedance detection signal (Vm) to the controller; and the controller is configured to determine whether there is an insulation impedance abnormity or not depending on the insulation impedance detection signal (Vm); and wherein the insulation impedance detection circuit is characterized in that the terminals of the voltage division circuit are electrically connected selectively to the first terminal of the impedance matching circuit via a switch; and wherein the voltage division circuit comprises a first resistor, a second resistor and the switch, wherein, two terminals of the first resistor are electrically connectable to the first AC terminal and the second AC terminal of the on-board charger respectively, one terminal of the second resistor is electrically connected to one terminal of the first resistor and another terminal is electrically connected to one terminal of the switch, and another terminal of the switch is electrically connected to the impedance matching circuit. terminals of the voltage division circuit are electrically connectable to a first AC terminal and a second AC terminal of the on-board charger respectively, and are electrically connected selectively to a first terminal of the impedance matching circuit; a second terminal of the impedance matching circuit is electrically connected to a first terminal of the biasing circuit, a second terminal of the biasing circuit is grounded, and a third terminal of the impedance matching circuit is electrically connected to an input terminal of the voltage sampling circuit; an output terminal of the voltage sampling circuit is electrically connected to the controller for outputting an insulation impedance detection signal (Vm) to the controller; and the controller is configured to determine whether there is an insulation impedance abnormity or not depending on the insulation impedance detection signal (Vm); and wherein the insulation impedance detection circuit is characterized in that the terminals of the voltage division circuit are electrically connected selectively to the first terminal of the impedance matching circuit via a switch; and wherein the voltage division circuit comprises a first resistor, a second resistor and the switch, wherein, two terminals of the first resistor are electrically connectable to the first AC terminal and the second AC terminal of the on-board charger respectively, one terminal of the second resistor is electrically connected to one terminal of the first resistor and another terminal is electrically connected to one terminal of the switch, and another terminal of the switch is electrically connected to the impedance matching circuit.