The utility model provides a reactor self-tightening seal-type material changing water level control structure which comprises a thermal insulation inner lining casing pipe arranged in an outlet connecting pipe, a drive connecting rod, a connecting rod end cover as well as a connecting pipe end cover, wherein the connecting pipe end cover is installed at one end of the outlet connecting pipe, which is far away from a reactor core hanging basket; one end of the drive connecting rod is connected with one end of the thermal insulation inner lining casing pipe so as to form a rigid entirety; the other end of the drive connecting rod penetrates through the connecting pipe end cover; the connecting rod end cover is installed on one end of the drive connecting rod which penetrates through the connecting pipe end cover, and is connected with the connecting pipe end cover through a seal structure; one end of the drive connecting rod, which is close to the connecting rod end cover, is provided with a threaded casing pipe in a sleeved mode; the outer side of the threaded casing pipe is threadedly connected with the connecting pipe end cover so as to form a drive pair; a seal gasket is also arranged between the drive connecting rod and the threaded casing pipe; and the connecting rod end cover is internally provided with a shock absorption spring. The reactor self-tightening seal-type material changing water level control structure provided by the utility model can pick and place the hanging basket in changing materials and meanwhile keeps the change material water level to be constant so as to enable the material change to be safe, provides favorable seal during the normal operation of the reactor, and is simple in structure and economical.