Abstract: A crystal plasticity finite element method was used to investigate the tension and the cyclic behavior of voronoipolycrystal copper in this paper. The tension simulation shows that polycrystalline copper has obvious response to the number of grains, and there are slip bands and necking observed in the copper. The symmetrical strain periodically exhibits the hardening and the Bauschinger effect. The Bauschinger effect is resulted from the interactions between grains in the copper, and could result in the residual stress after unloading. The unsymmetrical stress in polycrystalline copper cyclically shows that the average stress and the stress amplitude have important effects on the ratcheting behavior.