The utility model relates to a device for buffing and cleaning the inner wall of a pipe or tube and designs an automatic screw tube grinding machine, comprising a machine frame (1), a lifting platform (8) arranged on the machine frame (1), a motor (3) fixed on the lifting platform (8), a reducer (4) connected with the motor (3), a universal joint (5) connected with the reducer (4), a buffing bar (6) connected with the universal joint (5), a steel wire brush (7) arranged on the buffing bar (6) and a driving mechanism arranged on the bottom of the machine frame. The device can basically realize automatic screw tube buffing and cleaning with high cleaning efficiency and good effect, and the buffing steel wire brush can be used repeatedly. After the extrusion production is completed and the screw rod is pulled out, the grinding machine can be stretched into the screw tube for cleaning operation, which can avoid the waste of machine washing material and bad cleaning effect.