Abstract: In field-distortion gas spark switch, discharge channel between two electrodes can be conducted rapidly in argon gap, as abundant metastable atoms excite in argon. In this paper, a series of experiments to support the superiority of spark gap using argon gas mixtures were accomplished. The discharge characteristics of gas mixtures(SF6-Ar and N2-Ar) in spark gap were obtained under DC voltage. On this basis, we can get the optimized argon percentage of gas mixtures and figure out the breakdown characteristics of gas mixtures in spark gap. The spark gap using SF6-Ar can reach a lower jitter when the percentage of argon is higher than 20%. However there is no ideal performance using N2-Ar mixtures.