Abstract: The fracture toughness of 16MnR,20R and Q235B steel specimens were investigated respectively using three-point-bending experiments,and the fracture surface morphology was observed by SEM.The three samples exhibited ductile rupture behavior at room temperature.Delaminating phenomenon was observed in fracture zone of the three samples,but the delaminating phenomenon of fracture of 16MnR steel was obscure,while that of Q235B steel was obvious.When the direction of crack delaminating phenomena was not consistent with the direction of crack propagation,the delaminating phenomena provided resistance to the crack propagation,which increases the strength and toughness properties of the samples.