Disclosed is an improved cannula assembly with a balloon, the cannula assembly comprising a first sealing assembly and a second sealing assembly, wherein the second sealing assembly comprises a lower housing and a hollow cannula connected thereto and extending towards a distal end thereof, the first sealing assembly, the second sealing assembly and the hollow cannula comprise instrument passages communicated and substantially aligned with each other, and the hollow cannula comprises an inner cylindrical surface, an outer cylindrical surface and a cannula wall therebetween; the distal end of the hollow cannula further comprises an open cannula lip, the cannula lip comprises an inclined cylindrical surface between an open lip portion and a transition lip portion, and the inner cylindrical surface and the inclined cylindrical surface define an inclined cannula wall; the cannula assembly further comprises an inflatable and expandable balloon assembly, and an inclined balloon wall engages the inclined cannula wall
