The invention discloses a method for evaluating the sulfur corrosion state of a transformer copper coil. The method includes the steps that during the operation period of a transformer, the sulfur concentration in insulating oil is detected twice successively at a certain time interval, so that the change difference value of the sulfur concentration in the insulating oil at the time interval is obtained; the mass of generated cuprous sulfide is obtained through the change difference value of the sulfur concentration according to the substance conservation principle; then the average thickness of the cuprous sulfide deposited on the surface of the copper coil is calculated through combination of the mass of the cuprous sulfide and the known conditions of the density of the cuprous sulfide and the total surface area of the copper coil after the transformer leaves a factory; the sulfur corrosion state of the transformer copper coil can be determined according to the average thickness of the cuprous sulfide. The method is quick and accurate, and the corrosion state of a transformer copper winding subjected to electrified monitoring can be judged effectively. Through risk grade division and effective decision, safety risks caused by corrosive sulfur in the insulating oil of the transformer can be greatly lowered, and therefore good economic benefits and safety benefits are achieved.