A study was conducted on the spark channel resistance and thermal effect characteristics of a two-electrode gas-filled spark gap switch applied to a high-power repetition-rate Marx-type pulse power source. The influencing factors of the thermal effect of the spark gap channel resistance were analyzed, and the temperature and pressure changes inside the switch chamber under continuous repetition-rate working conditions were studied. The research results indicate that the pressure and temperature inside the switch chamber show a trend of rapid increase followed by slow increase and stabilization with the increase of working time. The increase of pulse current has a significant effect on the increase of heat deposition. Using the two-electrode spark gap switch developed in this article, 9 000 pulses were continuously operated under the conditions of peak conduction current of 14.7 kA and pulse width of 160 ns, and the discharge channel of the switch generated about 36.6 kJ of heat. During the current conduction time, the average resistance of the spark channel was calculated to be about 0.12 Ω through Joule heating effect.