Abstract: Metal active-gas welding (MAG) and tungsten inert gas welding (TIG) were used to weld NiCrMoV series of low-carbon bainitic high strength steel. Tensile tests were performed for two welded joints at different temperatures, and microstructure and tensile fracture of the joints were observed. The load-displacement curves of MAG joint were simulated by finite element software ABAQUS at different temperatures. The results show that the microstructure of welded seam of the low-carbon bainitic high strength steels was mainly composed of lath-like bainite and M/A constituent. In the range of -196 ℃ to 20 ℃, the strength of both welded joints gradually increased with the decrease of temperature. At -110 ℃, ductile fracture controlled the tensile fracture of TIG joint, however brittle fracture controlled the tensile fracture of MAG joint. The simulated load-displacement curves were consistent with the experimental ones.