Abstract: The welding joint of TP347H steel pipe of a high temperature superheater cracked several times. The cracking reasons were analyzed by macroscopic observation, chemical composition analysis, metallographic examination, scanning electron microscope and energy spectrum analysis, mechanical properties test and double-loop electrochemical potentiokinetic reactivation method test. The results show that the cracking property of TP347H steel pipe welded joint was intergranular stress corrosion cracking. The main causes of cracking were the sensitization of pipe heat affected zone caused by circulating heat during welding and the residual stress of welded joint.