Abstract: By the thermomechanical heat treatment friction-welding machine, the pipe body of 37CrMnMo steel and the pipe joint of 42CrMoA steel were welded, and the mechanical properties and microstructures of the joint were tested and analyzed. The experimental results show that the grain size in the full quenching zone can reach 8 grade, the partial quenching zone is narrow and covered by thermomechanical zone. After tempering treatment, the microstructure in partial quenching zone is the mixed microstructure of tempered sorbite and ferrite or the tempered sorbite with the grown carbide. The hardness in heataffected zones at pipe body and joint decreases by 6.9% and 4.2% respectively. The yield ratio of the joint is up to 0.905, its average impact energy is 95 J, and the fracture in tensile test appears at 37CrMnMo steel side. The mechanical properties of the joint meet the national standard of SY/T5561-1999 and America Petroleum Institute standard of APISPEC5D. The studied results indicate that the thermomechanical heat treatment can avoid the great reduction of impact toughness of weld and the decrease of hardness at the boundary of HAZ.