Abstract: The accumulator produced by a company cracked after one year of use. The cracking reason of the accumulator was analyzed by means of macroscopic observation, chemical composition analysis, mechanical property test, scanning electron microscope analysis and metallographic examination. The results show that there were microcracks in 35CrMo steel which was used to make the accumulator shell. When the accumulator was working, the pressure generated by the internal medium gas and hydraulic oil caused the micro cracks to gradually expand and penetrate the pipe wall, resulting in the accumulator cracking.