Abstract: The dynamic tension experimental technique of electromagnetically driven thin metal rings expansion was described, and quick-discharge switch and cut-off switch were improved to achieve rings free expansion. The approach is useful for studies on material constitutive relationship, dynamic fracture and fragmentation. The main circuit current was measured by Rogowski probe, and the expansion velocity was obtained from slit scanning cameras displacement measurement. The flow stress, strain, strain rate, expansion velocity and temperature rise of ring was obtained by electrodynamics analysis calculation.