ABSTRACT In this research, the correlation between the defect depth and the tangential piezomagnetic field of X70 steel was investigated. Tensile tests were carried out to measure the piezomagnetic fields on the surface of X70 specimens with different defect depths. The variations of piezomagnetic fields were compared to the simulation results of a theoretical model. The influences of loads and defect depths on magnetic parameters were discussed. This research demonstrates the potential possibility of evaluating the defect depth of ferromagnetic steels using piezomagnetic fields.