A method for obtaining internal side and external side insulation resistances of a relay, wherein the method is applied to a circuit comprising a battery pack, a main relay and a pre-charge circuit, the main relay comprises a main positive relay and a main negative relay, the pre-charge circuit comprises a pre-charge relay and a pre-charge resistor and is connected in parallel to both sides of the main positive relay, an insulation resistance obtaining circuit is connected between the battery pack and the main positive relay, wherein the method comprises steps of: controlling the insulation resistance obtaining circuit to output a low-frequency AC signal; when both the main relay and the pre-charge relay are switched off, obtaining an internal side insulation resistance of the main relay according to the low-frequency AC signal, wherein the internal side insulation resistance is an insulation resistance of the main relay at a side of the main relay close to the battery pack; if the internal side insulation resistance of the main relay is normal, controlling the pre-charge relay to be switched on; when the main relay is switched off and the pre-charge relay is switched on, obtaining an external side insulation resistance of the main relay according to the low-frequency AC signal, wherein the external side insulation resistance is an insulation resistance of the main relay at a side of the main relay away from the battery pack, wherein before controlling the pre-charge relay to be switched on, the method further comprises steps of: detecting whether the internal side insulation resistance of the main relay is greater than a first preset alarm threshold or not; if it is detected that the internal side insulation resistance of the main relay is greater than the first preset alarm threshold, determining that the internal side insulation resistance of the main relay is normal. controlling the insulation resistance obtaining circuit to output a low-frequency AC signal; when both the main relay and the pre-charge relay are switched off, obtaining an internal side insulation resistance of the main relay according to the low-frequency AC signal, wherein the internal side insulation resistance is an insulation resistance of the main relay at a side of the main relay close to the battery pack; if the internal side insulation resistance of the main relay is normal, controlling the pre-charge relay to be switched on; when the main relay is switched off and the pre-charge relay is switched on, obtaining an external side insulation resistance of the main relay according to the low-frequency AC signal, wherein the external side insulation resistance is an insulation resistance of the main relay at a side of the main relay away from the battery pack, wherein before controlling the pre-charge relay to be switched on, the method further comprises steps of: detecting whether the internal side insulation resistance of the main relay is greater than a first preset alarm threshold or not; if it is detected that the internal side insulation resistance of the main relay is greater than the first preset alarm threshold, determining that the internal side insulation resistance of the main relay is normal. detecting whether the internal side insulation resistance of the main relay is greater than a first preset alarm threshold or not; if it is detected that the internal side insulation resistance of the main relay is greater than the first preset alarm threshold, determining that the internal side insulation resistance of the main relay is normal.