Plug for heat transfer tube of nuclear power steam generator

The invention discloses a plug for a heat transfer tube of a nuclear power steam generator, which comprises a plug shell embedded in the heat transfer tube and an expansion block, the middle part of the plug shell is provided with a cavity matched with the expansion block, the outer wall surface of the expansion block is annularly provided with an expansion ring, and the expansion ring is pushed along the axial direction of the cavity to force the wall surface of the cavity to expand outwards along the radial direction. The outer surface of the plug shell and the inner surface of the heat transfer pipe form a sealing structure; a sealing ring, making contact with the inner wall of the heat transfer pipe, on a shell of a traditional drawing type plug is omitted, so that the wall thickness of the expanded expansion section of the plug shell is smooth and thin, and under the condition that equal thrust is applied to the expansion block, the thin wall of the plug shell is more easily extruded and expanded by the