Abstract: To evaluate the stress states of the components by the magnetic memory signal, Q235 steel defect asymmetrical samples were made. The characteristics of magnetic memory of Q235 steel in the three different states which are online-loading, online-unloading and offline-unloading under circle tensile stress have been studied. The results show that magnetic memory signals have different characteristics under different states. The curves in elastic range are different form that of initial stage and the curves of three states keep their shape on the whole elastic range respectively. In yielding stage, the curves of online-loading and online-unloading are beginning to appear wave peak and wave valley at the defect position. On the verge of necking, the curves of online-unloading appear a jump. From elastic range to necking, the curves of offline-unloading have no obvious change till fracture. It is feasible to preliminarily evaluate the stress state by the magnetic memory signal.