The present application discloses a circuit and a method for detecting insulation resistance. The circuit includes: a first voltage dividing module, a second voltage dividing module, a third voltage dividing module, a fourth voltage dividing module, a first switch module, a fifth voltage dividing module, a second switch module, a third switch module, and a detecting module, where the first voltage dividing module comprises a first voltage dividing unit and a second voltage dividing unit, and the third voltage dividing module comprises a third voltage dividing unit and a fourth voltage dividing unit. According to the embodiments of the present application, errors caused by fluctuations in the pull-up of the reference power supply can be avoided, and the accuracy of the circuit for detecting insulation resistance can be effectively improved.