The changes in the mechanical behavior of electric resistance welded(ERW) pipes before and after the cage roll forming process were investigated through tensile experiments.It is found that the Bauschinger effect does not exist in the pipe product,while the work hardening effect introduced by pipe-making is the direct cause of the mechanical changes.The prestrain introduced during different pipe-making processes are accumulative to the work hardening effect.And the increment of the yield strength for making  244.48×8.94 pipe is approximately 45 MPa,higher than that of hot-rolled plates.It is verified that the strain ε=tD-t is an efficient index representing the work hardening effect from the engineering viewpoint. The changes in the mechanical behavior of electric resistance welded (ERW) pipes before and after the cage roll forming process were investigated through tensile experiments. It is found that the Bauschinger effect does not exist in the pipe product, while the work hardening effect introduced by pipe-making is the direct cause of the mechanical changes. The prestrain introduced during different pipe-making processes are accumulative to the work hardening effect. And the increment of the yield strength for making  244.48 × 8.94 pipe is approximately 45 MPa, higher than that of hot-rolled plates. It is verified that the strain ε = tD-t is an efficient index representing the work hardening effect from the engineering viewpoint.