Disclosed is a cannula assembly with a movable and expandable 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 assembly further comprises an inflatable and expandable balloon assembly, a one-way valve assembly for inflating and deflating same, and a gas flow passage communicating the balloon assembly and the one-way valve assembly; the balloon assembly comprises a balloon lip and a balloon body connected thereto; and the balloon assembly further comp
