Abstract: Regarding the causes of pit defects on the inner wall of 4130X gas cylinder steel pipes, chemical composition analysis, mechanical property tests and non-metallic inclusion inspections were carried out on the gas cylinder steel pipes. Meanwhile, metallographic structure analysis, scanning electron microscope（SEM） and energy spectrum analysis were performed on the pits. The results show that the steel smelting and pouring processes were normal, and the pit defects were not caused by steel quality defects but were generated during the cold drawing process after hot forming. The pits were formed because iron oxide scale or other hard inclusions were pressed into the surface of the steel pipe during the drawing process, or the peeling of the lifting skin that originally existed on the surface of the steel pipe. During the manufacturing process, the preparatory work before cold drawing should be strictly controlled to prevent the recurrence of similar defects.