Abstract: During the cyclic pressure test on a certain aluminum alloy gas cylinder, the cylinder experienced leakage. The cause of gas cylinder leakage was analyzed using methods such as macroscopic observation, chemical composition analysis, mechanical property testing, scanning electron microscopy and energy spectrum analysis, and metallographic examination. The results show that the inner wall of the aluminum alloy gas cylinder was in contact with corrosive media, and pitting corrosion pits were generated on the inner wall of the gas cylinder. During the cyclic pressure test, pitting corrosion pits served as fatigue sources, causing fatigue cracking on the inner wall of the gas cylinder. The cracks continued to expand and penetrate the wall thickness, ultimately led to leakage of the aluminum alloy gas cylinder.