The steel pipe inner wall shot blasting machine adopts a special spray gun for strengthening sandblasting of steel pipe inner walls, especially a spray gun for strengthening the inner wall of austenitic stainless and heat-resistant steel pipes to improve their resistance to high-temperature steam oxidation corrosion. It has a nozzle and a spray rod, which are assembled at the front end of the spray rod. The nozzle has an outer tube and a guide core, and the front end of the guide core has a larger head end. A circular gap is formed between the nozzle guide core and the front end opening of the outer tube for spraying sand, pellets, and air mixture. During sandblasting, the energy of the air source and the steel pellets are concentrated in the narrow circular gap and sprayed, which can generate a uniformly distributed high-temperature oxidation and corrosion resistant hardening layer along the inner wall of the steel pipe. It can strengthen the inner surface of oil stains, rust, and black paint on the steel pipe after sandblasting and cleaning, and present a metallic luster to increase its surface area for workpiece spraying and painting. The spray rod is a straight austenitic stainless steel pipe, and its non plasticity in the length direction ensures that the shot blasting speed remains constant throughout the entire length of the steel pipe, generating a uniformly distributed hardening layer on the inner wall of the steel pipe; In addition, the flexible design with a large aspect ratio in the shape of the spray bar helps to automatically align the nozzle with the inner wall of the steel pipe for sandblasting.