Abstract: Microstructure, mechanical properties and corrosion resistance of 25Cr2Ni4MoV steel welded joint were compared and studied under conditions of pre-welding and post-welding quenching and tempering treatments. The quenching and tempering process was oil quenching at 920 ℃ for 1 h and tempering at 580 ℃ for 2 h. The welding process was manual electrode arc welding. The results show that by pre-welding quenching and tempering, the microstructure of the joint weld zone consisted of lath martensite, network δ-ferrite and M₂₃C₆ carbide. After the post-welding quenching and tempering, the δ-ferrite in the weld was dissolved, and the lath martensite, tempered sorbite and M₂₃C₆ carbide were formed. Under the post-welding quenching and tempering condition, the lath martensite in the weld was small and uniform, and the M₂₃C₆ carbide distributed in granular shapes on original austenite grain boundaries and martensite lath grain boundaries; the strength, impact toughness and corrosion resistance were better than those by the pre-welding quenching and tempering treatment.