The present invention discloses a plasma-based water treatment method, which comprises a reactor for storing and treating sewage, a high-voltage power supply and high voltage electrodes, wherein the high voltage power supply is adopted to generate an alternating current high voltage, the high voltage electrode is adopted to directly carry out discharging on a sewage load, high temperature and high voltage plasmas are generated through the discharging, and the plasmas contain a large amount of ions and OH free radical particles, such that organic matter molecules in plasma channels are subjected to complete high temperature pyrolysis or are subjected to advanced oxidation under an effect of the free radical so as to carry out chemical degradation. With the water treatment method of the present invention, physical contaminants, chemical contaminants, microorganisms and other contaminants in the water can be effectively removed, treatment cost is low, and a significant removing effect is especially provided for high concentration organic matters in the water. In addition, the water treatment method of the present invention further has advantages of stable discharging voltage, uniform treatment, safety and reliability, wherein water treatment efficiency is improved while energy consumption is substantially reduced.