Abstract: A company used hot-rolled steel plate to produce pipes by high frequency longitudinal resis tance welding,the welded pipe end cracked after cutting.By means of macroscopic observation,chemical composition analysis,metallographic inspection and fracture analysis,the reasons for cracking of welded pipe were analyzed.The results showed that in the welding process,the input power was too high due to the excessive welding current,which caused the welding seam temperature to be too high.Thick Widmanstätten microstructure and a large number of holes were formed at the weld,which led to cracking of welded pipe.