Abstract: A repetitive Tesla pulsed power generator with 1 MV, 40 ns output was used to study the resistances of gas spark switch in nitrogen under high gas pressures and large gap. With the switch regarded as a RLC circuit, the resistances were computed under different gas pressures, by using the measured voltages of the pulse forming line and conical transmission line. The results show that the resistances reduce quickly during the formation of discharging channels, and eventually reach ohm level. Experimental and theoretical results are compared to check if Barannik, Rompe-Weizel, Demenik, Toeple, and Vlastos formulas are applicable. The Rompe-Weizel formula is modified by changing a different constant.