Abstract: The common heat treatment process of pressure vessel was introduced. The effect of post-weld heat treatment on mechanical properties of welded joints of V improved steel (2.25 Cr-1 Mo-0.25 V), P91 steel and 07 MnNiMoDR steel was described. The effect of heat treatment above A_c3 line on the impact toughness of hot forming head weld and electroslag welded joint was emphasized. The improvement of other properties of welded joints (weld metal) by post-weld heat treatment was introduced from aspects of fracture toughness, creep property, stress corrosion resistance and fatigue strength. It was hoped that the customary term of "heat treatment to improve the mechanical properties of materials" in relevant standards would be changed to "heat treatment to improve the mechanical properties of welded joints".