Provided is a method and device for obtaining internal side and external side insulation resistances of a relay. The method includes: controlling an insulation resistance obtaining circuit to output an AC signal; when both a main relay and a pre-charge relay are switched off, obtaining a first phase shift of the AC signal between two sampling points according to first collected electrical signals; obtaining an internal side insulation resistance of the main relay according to the first collected electrical signals and the first phase shift; 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 a second phase shift of the AC signal between the two sampling points according to second collected electrical signals; and obtaining an external side insulation resistance of the main relay according to the second collected electrical signals and the second phase shift.