In this work, we studied aging and fatigue behaviors of 1.0 mol%Cu-modified (Na0.5K0.5)NbO3 lead-free ceramics with double-loop-like characteristic, and found an interesting result of electric field cycling induced large electrostrain in the aged samples. After the aging treatment, the hysteresis loop closes totally and constricts completely at zero electric field, accompanying with a large nonlinear electrostrain of about 0.26%. More interestingly, the electrostrain in the aged sample is sensitive to the field cycling, which is pushed to a higher level of 0.47% approaching that of some Pb-based antiferroelectric materials. A microscopic model of the domain switching-related electrostrain effect is proposed to explain the field cycling induced large electrostrain in the aged samples. It can be identified due to the weakening of intrinsic restoring force for reversing the switched domains, induced by the point defects (defect dipoles) migration aligning along field direction during cycling, evident by the gradually opened hysteresis loop with cycling.