This paper studies the arc discharge phenomena in a small gap-length（<0. 1mm） vacuum gap

which is closely related to the multiple reignition process. It is found that the discharge phenomena can be described by the relation between the cold breakdown voltage and gap-length

hot voltage withstanding strength and gap-length

and the number of half-frequency arcing discharge. It is obtained that CuCr has the highest cold breakdown strength which is three times of the AgWC’s and is not sensitive to circuit parameters. A model based on energy dissipation of the circuit is developed to calculated the high-frequency arcing period.