Abstract: The tensile tests for both hadfield steel and 18-8 stainless steel were carried out at room temperature.The work hardening behaviors of both steels were analyzed by Hollomon method and Crussard-Jaoul method.The results show that the Crussard-Jaoul method could better describe and characterize the characteristics (of work hardening behavior) and mechanism of 18-8 stainless steel and hadfield steel as compared with Hollomon method.The deformation mechanism of 18-8 stainless steel was dislocation slip.The deformation mechanism of hadfield steel was also dislocation slip when the strustrain was below 0.07,but twinning would occur when the strustrain was over 0.07.It was the occurrence of twinning that led to unusual work hardening at large strain in hadfield steel and 18-8 stainless steel.