Abstract: A sheath includes: a ring-shaped inner layer structure, a ring-shaped outer layer structure and a frame structure, which can be radially expanded with the inflation of a balloon inside the inner layer structure. When the inner layer structure, the frame structure and the outer layer structure are not radially expanded, a radial dimension of an inner channel of the inner layer structure is at a first radial dimension, and the first radial dimension is greater than or equal to a radial dimension of the balloon that is not inflated. After the inner layer structure, the frame structure, and the outer layer structure are radially expanded, and the balloon is removed or deflated, the radial dimension of the inner channel of the inner layer structure is at a second radial dimension, and the second radial dimension is greater than the first radial dimension.