The invention discloses a thickened oil three-phase separator which is used for removing free water and reducing viscosity by adding thin oil and is used in oil fields and mine fields. The thickened oil three-phase separator is composed of an outer shell, a separation cavity, a gas-liquid pre-separation barrel, a liquid distributor, an inlet, a gas communication pipe, a gas outlet, a gas distribution bag, separation filler, a thin oil adding distributor, a thin oil distribution mouth, a chemical agent distributor, a chemical agent distribution mouth, an oil spilling weir plate, a water outlet, an oil outlet, an oil cavity, a thickened oil and thin oil mixer, and the like. A thin crude oil distributor and a thin oil distributor are arranged in the separator, and then thin oil is enabled to permeate into a certain position inside the separation cavity, and then the viscosity of thickened oil is reduced after the free water is removed. The chemical agent distributor and the chemical agent distribution mouth are arranged in the separator, chemical agents are enabled to permeate into a certain position inside the separation cavity, and chemical demulsification is carried out on the thickened oil after the free water is removed. The thickened oil and thin oil mixer is arranged at the position of the oil cavity of the oil outlet of the separator, mixing degree of the thickened oil and the thin oil is increased with methods such as a mechanical vibration method, and the thickened oil is enabled to be discharged out of the separator smoothly.