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The limited lifetime in a high current is the main drawback of spark-gap switches. Electrode replacement is an easily suggested method to extend the lifetime. In order to perform electrode replacement, thermal damage caused by heating effect should be prevented at the static electrical contact interfaces between the electrodes and the holders. Based on the Holm model, the Hertz formula, and the heat conduction theory, a mathematical model of the contact temperature rise is proposed in this paper. This mathematical model can prove quantitatively that the pulse-current integral (action integral), material physical properties, and mechanical characteristics of spark-gap switches are key parameters affecting the temperature rise. The action integral is determined by the electrical parameters. Material physical properties include the thermal conductivity, the specific heat, the density, the electrical resistivity, the elasticity modulus, and the Poisson ratio. Mechanical characteristics of spark-gap switches include the contact radius/area, the contact force, and the contact surface roughness. The implementation of electrode replacement depends on the reasonable configuration of these key parameters. The experiments in a 1.2-MJ power supply module give that the phenomenona correspond with our analysis. Based on the analysis in this paper, an electrode holder structure is proposed as a practical solution for extending the useful lifetime of spark-gap switches with graphite electrodes.