Abstract: Using optical microscopy, tensile, impact and hardness tests, the microstructure and property of the welded X100 pipeline steel joint were studied. The results show that the microstructure was coarse proeutectoid ferrite and granular bainite in the coarse-grained zone of the joint, fine ferrite in the fine-grained region, and fine-grained ferrite, coarse-grained acicular ferrite and granular bainite in the incomplete recrystallization region. The average tensile strength of the joint was 576 MPa, which got to about 80% of the base materials. The tensile fracture occurred in the welding seam. The impact energy in the welding seam and heat affected zone were 198 J and 259 J, respectively. The maximum hardness value was 316 HV in the weld zone. The phenomenon of softening appeared between the critical heat affected zone ( ICHAZ) and the subcritical heat affected zone (SCHAZ).