The problem of oilpaper insulation partial discharge has attracted widespread attention in the industry. In order to explore the characteristics of partial discharge under ACDC composite voltage, this paper builds a measurement platform and designs four typical types of discharge model for oilpaper insulation defects: air gap discharge, suspension discharge, and cylindrical surface discharge models. The experimental results of these four kinds of partial discharges indicate that, the partial discharges of the four typical defects will change differently under different composite voltage ratios. The variation characteristic of average discharge for the first three defect types are opposite to which of DC component and positive to which of initial voltage at the initial period. Compared with the other three typical defects, the initial voltage of partial discharge in the suspended insulation discharge model under AC and DC mixed voltage is obviously increased, and the average discharge under AC voltage is reduced. The results obtained provide basic data for the application of partial discharge tests to determine the effect of the type of commutation transformer defect and the voltage form on the partial discharge.