Abstract: A multi-gap rail switch is introduced with its configuration and self-breakdown experiments. The streamer theory gives a Raether criterion which is used to estimate if the gap can be broken down. An equation about self-breakdown voltage is obtained from the criterion. When the switch has high gas pressure, there is a visible difference between experimental data and empirical relation. Breakdown voltage nonlinearly increases with increasing pressure, and by analyzing the experimental condition and data, its reason may be corona from electrode surface. Because of special geometry of the switch, the corona can not only make the electric field uniform but also decrease the distance of A-K gap under high voltage and high gas pressure.