Abstract: The deformation law in fitting-manufacture thermal process of an X70 grade pipeline steel was investigated using a Gleeble-1500 tester.There were two kinds of stress-strain curves of both dynamic recovery and dynamic recrystallization in thermal deformation process.Under the condition of high temperature and low strain rate,dynamic recrystallization occurred.The thermal deformation equation was =4×10-8σ10.27p exp(-Q/RT) and relations between σp of εp and Z were ln σp=1.869+0.093lnZ and ln εp=-1.291＋0.021 lnZ respectively.The volume fraction of dynamic recrystallization was Xd=1-exp-1.51(ε/εp-0.83)1.22.