Abstract: From thermodynamics, the electrode erosion process of high-power gas spark gap switch is analysed in theory. The simplified mathematical model is built and solved numerically, the relations between electrode erosion depth and some characteristics of electrode materials such as density, specific heat, melting point, boiling point, thermal conductivity, and so on, are studied. The capabilities of three common electrodes (made of Cu, W, and Al) to resist erosion are compared, which indicates that a ranking of the erosion rate for three materials, from least to greatest, is W, Cu, Al.