Abstract: The gas-solid interface between SF₆ gas and the epoxy resin-impregnated paper capacitor core inside the resin-impregnated paper bushing (RIP Bushing) is the weak point of insulation inside the bushing where discharges are likely to occur. In order to study the long-time flashover discharge characteristics and its influencing factors at the gas-solid insulation interface inside the dry-type bushing, we build an experimental platform for flashover characteristics, and test the surface charge distribution of epoxy-impregnated paper specimens under the influence of different surface states and particles, revealing the influence mechanism of various factors on the surface electric field and flashover characteristics. At the same time, a long-time pressurization experiment is conducted to obtain the discharge characteristics by manufacturing defects core specimens. The results show that there are highly dispersed fiber protrusions at the gas-solid interface of the bushing in the high-voltage side area, in which particles can be easily attracted during operation. Under the action of DC voltage, charge accumulation and electric field distortion will cause weak initial partial discharge. Besides, the long-term voltage action intensifies the charge accumulation, further increases the degree of electric field distortion, gradually increases the frequency and amplitude of PD, and eventually leads to penetrating flashover discharge. The research results can provide theoretical and experimental basis for optimization of the surface treatment process of the resin-impregnated paper bushing capacitor core and the formulation of the suppression measures for flashover discharge under long-term direct current.