The invention relates to an internal expansion clutch which comprises upper and lower brake belts, a fixed bracket, a normally-closed hydraulic oil cylinder, a connecting rod and an adjusting screw rod; an outer port in one end of the lower brake belt is in pin connection with the fixed bracket, an outer port in one end of the upper brake belt is in pin connection with the adjusting screw rod, the other ends of the upper brake belt and the lower brake belt are hinged to each other, and the upper brake belt and the lower brake belt are supported outside the fixed bracket in a circumferential shape; one end of the normally-closed hydraulic oil cylinder is in pin connection with the fixed bracket, the other end of the normally-closed hydraulic oil cylinder is hinged to one end of the connecting rod, the middle of the connecting rod is in pin connection with the fixed bracket, and the other end of the connecting rod is connected with a fixed screw rod. The internal expansion clutch provided by the invention has the benefits that the connecting rod is pushed through oil going in and out of the normally-closed hydraulic oil cylinder, so that a drive sleeve at the other end of the connecting rod drives the fixed screw rod under the action of a limiting block, and the upper brake belt for connecting the fixed screw rod is folded inwards to loosen a brake hub or unfolded outwards to be close to the brake hub; a drive structure is compact and stable, so that the use safety and reliability and the service life can be effectively ensured.