A supporting device for surgery has a discharge device including a first tubular structure and a relief valve module connected with the first tubular structure. The first tubular structure can be used to encapsulate a scalpel device, and the relief valve module can be connected to a second tubular structure allowing the substance generated during a surgery to be removed. The relief valve module has a rotating assembly used to remain stable when the scalpel device rotates to prevent the second tubular structure twine around the scalpel device during the surgery.