Polycrystalline Cr-Ni alloy have received extensive attention due to their great attractive mechanical properties. However, the sensitivity of deformation behavior to crack appearance is lack of investigation. In this study, the effects of the crack positions on the mechanical properties and deformation mechanism development of polycrystalline Cr-Ni alloys are investigated by using molecular dynamics simulation under tensile test. The crack position plays a dominant role and decides the direction and position of shear strain that leads to direction ductile fracture. The shear strain grows from the roof of the crack and creates with the horizontal direction an angle of about 45° or 135° depend on the crack positions.