The invention relates to a liquid medium non-transfer arc plasma gun. The liquid medium non-transfer arc plasma gun mainly comprises a negative electrode tube, a positive electrode tube, an insulatorand a ceramic ring, wherein the negative electrode tube is arranged in a rear gun body of the plasma gun, a plurality of liquid medium through holes are formed in a rear end part of the negative electrode tube, the positive electrode tube is arranged in a front gun body of the plasma gun, the insulator is fixedly arranged between the front gun body and the rear gun body, a plurality of connectionholes are formed in the insulator, the ceramic ring is fixedly arranged in the insulator and is used for restraining a plasma arc generated between the negative electrode tube and the positive electrode tube. A liquid is used as a medium, enough ion gas can be provided only by a few amount of liquid, the volume of the liquid after being boiled and evaporated in the negative electrode tube can be expanded by thousands of times, a gas medium can be completely substituted, moreover, the effect is remarkably improved compared with the gas medium, an air path is not needed to be considered during the process of designing the non-transfer arc plasma gun, and the gun body structure is simplified.