The invention relates to a test device for testing insulating characteristic of oilpaper and a test system thereof. The test device comprises an oil storage barrel, a cover and a box body; wherein the oil storage barrel, the cover and the box body are successively arranged. The box body comprises an inner box body which is connected with the cover, and an outer box body that is connected with the inner box body. The inner box body is provided with a fixed part, a detachable electrode and an adjusting member from inside to outside. The test system comprises a double-layer supporting platform, the test device which is arranged at the upper layer of the supporting platform, and a heating oil tank which is arranged at the lower layer of the supporting platform. The test device can be used for observing partial discharge and breakdown of cardboards with different thicknesses or oil gaps at different voltage types and different voltage grades in different electrode types and different environments. Related parameters are recorded and furthermore an insulating mechanism is disclosed. The test device well simulates a plurality of insulating faults which may occur in actual operation of a transformer. The research result of the test device can be directly applied for guiding construction of an ultra-high-voltage power transmission system.