Abstract: The cause responsible for nonconformance of yi eld strength property of the Q235B coil for SAWH pipe-making are investigated by means of macroscopic morphology analysis, CVN impact test, chemical composition analysis, Vickers hardness testing and metallographic examination, etc. The analysis result reveals that the micro- structure of the nonconforming sample is of coarse ferrite and pearlite structure. It is just such inhomogeneous structure that mainly causes the yield strength property nonconformance of the Q235B hot rolled coil.