Abstract: The pre-fire of gas switches is the unexpected breakdown at triggered mode, which is the main factor restricting the development and engineering application of linear transformer driver (LTD). In this paper, the dispersion of breakdown voltage as well as pre-fire rate of multi-gap gas switches under typical working pressures of LTD was investigated and reported. A simplified gas switch was designed to measure self-breakdown voltage at higher gas pressures, and the cumulative distribution function of self-breakdown voltage considering uneven gap voltage distribution was derived. The self-breakdown voltage distribution characteristics of multi-gap switches under LTD working pressure were calculated and experimentally verified. The estimated pre-fire rate was obtained by using peak-over-threshold method to fit the Weibull distribution of small probability pre-fire events under low working coefficients. The measured pre-fire rate was obtained by a 10 000 triggering test. The results show that the dispersion of the self-breakdown voltage of the switch increased with air pressure. Measuring the self-breakdown voltage at low air pressure can not extrapolate the pre-fire rate at high pressure under actual working conditions. When the working coefficients of the gas switch were 65% and 60%, the estimated pre-fire rates were 1.44 \times 10^ - 4 and 3.01 \times 10^ - 5, which were close to the experimental results of the 10 000 triggering test, verifying the feasibility of the estimation method.