The oil paper/oil interfaces in transformer oil paper materials with different aging degrees have different space charge accumulation characteristics under DC electric field, which can characterize the aging state and insulation per-formance of oil paper insulation system to a certain extent. In this paper, one type of insulating paper and two types of insulating oil materials are used to make oil paper/oil double-layer samples respectively. The space charge distribution and the change of polarization/depolarization current of the combined samples of different oil paper materials are tested respectively. The characteristics of interface charge are analyzed according to the space charge, the interface barrier parameters are extracted, and the change law of collapse current is studied by polarization/depolarization current, and the correlation between the trap parameters and the trap parameters in the sample is found.