With the application of domestic X70 pipeline steels in the project of “gas transmitting from west to east”, they mostly serve in wet environments with H_2S. In order to prevent pipeline steels from more loss in advance of cracking, the study on sulfide stress corrosion cracking (SSCC) properties for domestic X70 pipeline steels became more and more important. Therefore microstructures of base metals and welds were tested and analyzed, and slow strain rate test (SSRT) was further adopted to study the resistance of SSCC of X70 steels and welding joints, the effect of content of H_2S on corrosion properties of pipeline steels was discussed. The results revealed that with the increasing of H_2S concentration, resistance of SSCC would increase. When H_2S concentration was 50×10~(-4)~0_0, brittleness coefficient of base metal was 19.95~0_0,and brittleness coefficient of welding joint was 59.19~0_0. As far as SSCC was considered, if it was assumed safe value when brittleness coefficient was 25~0_0, domestic X70 steel base metals were safe ,while its welding joints were not in the medium with 50×(10~(-4)~0_0 )H_2S concentration.