It has a great tendency to the problem of environmental cracking under the service condition of LPG containing wet H2S surpassing the lowest allowance for steels. In order to quantitatively evaluate the cracking susceptibility on this steel in the wet H2S environment, the pre-fatigue crack M-WOL specimen stress corrosion cracking tests in three H2S concentrations were performed under the different welding conditions, and in safety performance analysis of equipment, and preventing countermeasure had been proposed. The results show that the presence of H2S considerably influences the corrosion process of SPV50Q steel and its corrosion rate increases with increasing H2S contents. With decreasing pH and increasing in temperature of the testing solution, the corrosion of this steel is also enhanced. Although the semicircular diameter of capacitive loop increases with immersion time, its variation amplitude is not obviously great and begins to diminish after certain periodic time, suggesting that the sulfide film formed on the surface can not effectively prevent SPV50Q steel for avoiding the further corrosion.