The utility model relates to an insulation detection device for the high voltage bushing of a transformer. The insulation detection device comprises a frequency conversion power source with adjustable frequency and voltage, an adjustable resonance reactor, a voltage detection unit, a current detection unit, and a measuring and control unit. The insulation detection device is characterized in that the frequency conversion power source is connected with a high voltage bushing to be tested via the adjustable resonance reactor; the high voltage bushing to be tested is connected with a ground via the current detection unit; the voltage detection unit is disposed between the output terminal of the adjustable resonance reactor and the ground; and the measuring and control unit is connected with the frequency conversion power source, the adjustable resonance reactor, the current detection unit and the voltage detection unit, respectively. According to the utility model, the frequency of the power source can be changed, the inductance value of the resonance reactor can be changed, different compensation capacitors are adopted, such that 10kV testing voltage with different frequencies can be flexibly obtained through series resonance, and the volume and the weight of equipment are reduced.