Abstract: A precipitation hardened stainless steel spring experienced brittle fracture. The cause of the spring fracture was analyzed using macroscopic observation, hydrogen content testing, metallographic examination, hardness testing, scanning electron microscopy and energy spectrum analysis. The results show that during the surface passivation treatment, hydrogen permeation occurred in the spring. After dehydrogenation treatment, the spring still contained a small amount of hydrogen element. Under stress, hydrogen induced brittle microcracks began to appear in the spring, and the cracks continued to expand, ultimately led to overload fracture of the spring.