Based on a surface discharge model, partial discharge experiment in the simulation transformer tank is carried out to research the development characteristics and characteristic parameters’ variation law of surface discharge in transformer oil-paper insulation, and the variation characteristic of dissolved gases in oil in the discharge process is emphatically researched. The results show that the surface discharge value increases at the beginning stage of the discharge process, and reaches its maximum after 2~3 h, then it decreases gradually. As the development of partial discharge, the absolute generation speed of CO fluctuates around a certain value with small variation. While, the absolute generation speeds of H2 and CH4 increase first and then decrease, and the variation of discharge spectrum is highly similar to the variation of oil-dissolved gas’ absolute generation speed.