The mechanical response of a bi-crystal model with a 90° grain boundary under external compressive and tensile loading parallel to the boundary plane normal was investigated with molecular dynamics simulations.The grain boundary was found to migrate along two opposite directions upon compressive and tensile straining,with the formation of inter-connected coherent twin boundary and basal/prismatic boundary.The atomic details of such grain boundary migration were unraveled,which indicated the role of interface dislocations.The temperature effect was also discussed.