The invention relates to a maintenance-free respirator device applied to oil-filled electrical equipment and an operation method. The maintenance-free respirator device comprises a breather tank, wherein the breather tank is filled with a drying agent; a longitudinal breathing pipe and a helical electric heating assembly are arranged in the breather tank; the helical electric heating assembly is encircled on the peripheral part of the breathing pipe; the upper end and the lower end of the breathing pipe respectively penetrate out of the breather tank; a first electromagnetic valve is arranged at the upper end, which penetrates out of the breather tank, of the breathing pipe; a breathing pipe seal plate which is connected through a first spring resetting assembly is arranged at the lower end, which penetrates out of the breathing pipe, of the breather tank; a plurality of air guide holes are formed in the upper part, in the breather tank, of the breathing pipe at intervals; a vacuum supply pipe is arranged at the upper part of the breather tank in a penetrating manner; and the lower end of the vacuum supply pipe is connected with a vacuum supply pump which is used for extracting water vapor which is generated by heating the drying agent in the breather tank after moisture absorption in a saturation state through a second electromagnetic valve. The respirator device is compact in structure; the drying agent can be rapidly dried after moisture absorption in the saturation state; and meanwhile, the operation method is simple.