The utility model relates to a barrel-type oil tank of a transformer. The barrel-type oil tank comprises a tank body, a clamping piece, a lifting screw rod and a second insulating structure, the box body is of a hollow cylindrical structure and is provided with a containing cavity, and the inner wall of the containing cavity comprises a top wall and a bottom wall. The clamping piece is contained and fixed in the containing cavity, the clamping piece and the inner wall of the containing cavity are arranged in a spaced mode, the clamping piece is provided with a top end and a bottom end oppositeto the top end, and a grounding wire is arranged on the clamping piece. The hanging screw is contained and fixed in the containing cavity, and the top end is fixedly connected with the top wall through the hanging screw. And the lifting screw rod is arranged between the lifting screw rod and the top end, so that the top end is insulated from the box body. The second insulating structure is arranged between the bottom end and the bottom wall, so that the bottom end is insulated from the box body. The transformer barrel-type oil tank provided by the utility model has better reliability in measuring the insulation resistance of the clamping piece.