Abstract: Four coaxial electrodes with identical shape but different surface characteristics are made by common surface treatments, including sanding, wool polishing, metal electroplating and nonmetal electroplating. The relationship between different surface characteristics and the insulation characteristics of the glycerol medium is studied by experiments. A thyristor controlled air-core pulse transformer with a maximum output voltage of 500 kV and the rising time of 26 s is built. The experimental results show that the four kinds of electrodes have significantly different microcosmic morphologies, resulting in different breakdown characteristics of the glycerol between the electrodes. Under the same charging voltage, the average breakdown strength of the glycerol is 210-260 kV/cm. Compared with the conventional sanded electrodes, the breakdown strength of electrodes disposed by wool polishing, metal electroplating and nonmetal electroplating can be increased by 14.51%, 11.60% and 19.67% respectively. Due to their much higher surface uniformity, the highest breakdown strength between nonmetal electroplating electrodes can reach up to 288 kV/cm, which is 33.09% larger than the average value of the control group.