There are significant differences between the calculation results and experimental results by using J. C. Martin empirical formula to estimate the breakdown electric field for hundreds of kV/cm electric field and nanosecond pulse. To improve the design of pulsed gas switch and adjustment of working conditions, the relationships between the breakdown electric field and time delay and the experimental parameters based on the classical empirical formula is established. The empirical formula of breakdown electric field and time delay for SF₆ gas switch under nanosecond pulse and hundreds of kV/cm electric field is presented. It is indicated that the slope of pulse will affect the breakdown characteristics of nanosecond pulse in high electric field and the breakdown electric field is correlated with the breakdown time delay. The differences between the calculation results and experimental results are caused by the experimental conditions. The fitting expression of empirical formula can give more guidance for the design of output switch in the electromagnetic pulse simulator.