In order to clarify the distortion effect of space charge on the electric field intensity of insulation paperboard and the effect mechanism of degradation degree of paperboard and space charge, the bipolar carrier transport model is adopted to simulate characteristics of space charge in insulation paperboard with different degradation degree. When DC voltage is applied in the insulation paperboard with the same aging condition, the mono-polar charge accumulates in the paperboard, and the distribution range of positive polarity charge is significantly narrower than negative polarity. When the applied voltage time increases, the electric field distortion rate in paperboard also increases. When the degradation degree of insulation paperboard deepened, both the trap density and trap depth increase, resulting in a large amount of space charge accumulate in the paperboard adjacent both electrode sides, which further weakens the electric field intensity at the boundary of the paperboard and the electrode, and intensifies the field intensity distortion inside the paperboard. Moreover, the more serious the deterioration of insulation paperboard, the more prominent the distortion effect of space charge on the electric field. The degradation of paperboard is accelerated. On the other hand, the breakdown fault of paperboard is prone to be induced. The conclusions provide reference for the design of oil-paper insulation.