The invention discloses an automatic sand blasting machine for an inner wall of an elongated pipe. A sand blasting mechanism is arranged on a rack and comprises a sand blasting pipe, a sand returningpipe and a sand storing tank, wherein the sand blasting pipe and the sand returning pipe have No. 1 positions matched with two ends of a pipe fitting to be subjected to sand blasting as well as No. 2positions separated from two ends of the pipe fitting to be subjected to sand blasting; when the sand blasting pipe and the sand returning pipe are in the No. 1 positions, the sand blasting pipe, thepipe fitting to be subjected to sand blasting, the sand returning pipe and the sand storing tank form a cyclic sand blasting runner; the sand blasting mechanism controls the sand blasting pipe and thesand returning pipe to be subjected to press fitting with the two ends of the pipe fitting to be subjected to sand blasting to perform sand blasting; in the sand blasting process, the sand is not easy to leak from the two ends of the pipe fitting, and the sand and scales in the pipe fitting to be subjected to sand blasting are blown into the sand storing tank through the sand returning pipe and can be continuously cleared; and when the scales are completely removed, the sand blasting mechanism controls the sand blasting pipe and the sand returning pipe to be separated from the two ends of thepipe fitting to be subjected to sand blasting, so that the clearing is convenient, the environment is prevented from being polluted, the sand is recycled, and the cost of an enterprise is reduced.