The invention relates to the field of dissolved oxygen content detection, in particular to a three-electrode electrochemistry dissolved oxygen sensor. The sensor comprises a cylindrical shell of the sensor, a replaceable oxygen permeation membrane, a membrane cover, a gold electrode, a sliver electrode and a platinum electrode, wherein the gold electrode is arranged in the cavity of the cylindrical shell to serve as a working electrode, the sliver electrode serves as an auxiliary electrode, the platinum electrode serve as a sliver protection electrode, and the silver electrode, the gold electrode and the platinum electrode are independently connected with a polarization circuit through leads; the cavity of the cylindrical shell is full of a liquid reaction electrolyte, wherein the electrolyte reaction liquid comprises the following ingredients in parts by weight: 74.55 parts by weight of potassium chloride, 0.561 parts by weight of potassium hydroxide and 1000 parts by weight of water.By use of the electrochemistry dissolved oxygen sensor disclosed by the invention, in a measurement process, oxygen in a water sample is not consumed, detection accuracy is improved, an auxiliary electrode adopts a double-helix structure to increase a contact area with the electrolyte, the response speed of the sensor is improved, the sensor adopts a three-electrode system structure, the electrolyte in the electrolyte is not consumed, the silver of the auxiliary electrode is not consumed, and the service life is greatly prolonged.