Abstract: The paper analyzes and discusses the cause of sulfide stress cracking (SSC)and its preventive measures, and points out that the interactions among the hardness of tank metal, stresses arisen during installing and operating, H₂S concentration and water content of LNG results in SSC of LNG spherical tank. Therefor, three counterrneasures to pvevent the LNG spherical tank from SSC should be taken: ①selecting the metal with proper hardness to fabricate spherical tank; ② reducing the stresses of spherical tank if possible; and adopting heat treatment or hydrostatic test to relief stress; ③ installing sweetening and dehydrat- ing devices.