Abstract: In order to trigger the two-electrode gas switch without a trigger electrode, not only a high magnitude, fast rise time output pulse is needed but also high reliability is required for the switch trigger in high power system. A six-stage Marx trigger was introduced to solve the above technical and reliability problems. A pulse voltage with fast rise time and high magnitude was obtained by establishing a multi-stage pulse forming circuit and the operating parameters were determined by the method combining experiment measurement with probability model analysis. The results demonstrate that, both the self-trigger rate of Marx trigger and the success rate of triggering gas switch accord with the two-parameter Weibull distribution model established based on experimental data. The output voltages magnitude can reach 120 kV and rise time is less than 20 ns, when the under-voltage ratio is 65%, the operating voltage is 13.5 kV, and the absolute gas pressure is 0.35 MPa. The calculated self-trigger rate is less than 0.000 1% and the calculated success rate of triggering gas switch is higher than 99.999 9%.