This application discloses a cannula comprising the movable and inflatable balloon, which includes the first seal assembly and the second seal assembly, which comprises the lower outer casing and the hollow sleeve connected thereto and extending to the distal end. The first seal assembly, the second seal assembly and the hollow sleeve include the instrument access that is communicated and substantially aligned, the hollow sleeve including the inner cylinder surface, the outer cylinder surface and the sleeve-wall therebetween； the distal end of the hollow sleeve further includes the open sleeve lip； the cannula further includes the inflatable balloon assembly, the one-way valve assembly for inflation and deflation, and the gas access connecting the balloon assembly and the one-way valve assembly； the balloon assembly includes the balloon lip and the balloon body coupled thereto.
