The work aims to analyze and explore the hydrogen trapping efficiency in base metal and welded joint of X70 MS pipeline steel and its influence mechanism on sulfide stress corrosion cracking (SSCC) susceptibility. According to NACE TM 0177 standard, the threshold stress (σscc) of SSCC in the base metal and welded joint of X70 MS pipeline steel was obtained by uniaxial tensile testing, and the fracture morphology, the surface morphology after hydrogen microprint and the EBSD of the cracks area after electrochemical hydrogen charging were observed by field emission scanning electron microscope (FE-SEM). The dynamic parameters of hydrogen permeation in the base metal and welded joint were measured by the improved D-S double cell hydrogen permeation technology and Letry stress corrosion tester. The σscc of SSCC in base metal and welded joint of X70 MS pipeline steel was 362.1 MPa and 338.4 MPa respectively, and the fracture showed brittle fracture characteristics. Compared with the base metal, the hydrogen permeation flux J∞ and apparent hydrogen concentration Capp of welded joint were larger, the effective hydrogen diffusion coefficient Deff was smaller, and the trapped lattice hydrogen, reversible hydrogen and irreversible hydrogen concentration were higher. The welded joint of X70 MS pipeline steel has higher SSCC susceptibility than the base metal. On the one hand, the grain boundary and sub-boundary of lath bainite in the welded joint are hydrogen diffusion channels and traps, which have higher hydrogen trapping efficiency; on the other hand, there are more {101}//ND orientation grains in the welded zone, which are easy for transgranular extension of cracks. Under the combined action of force and reversible hydrogen, the cracks can easily propagate through these grains.