In order to reveal the influence of grain boundary (GB) orientation on the plastic deformation of copper bicrystals (CB),first,a CB block was fabricated via the diffusion welding.Then,the equal- strain compression of CB in horizontal and vertical grain boundaries was carried out on a compressing test bed.Moreover,the microscopic morphology near the GB was observed and analyzed.The results show that different grain boundary orientations affect the slipping deformation of CB in different ways,and that,as compared with the CB in horizontal grain boundary,the vertical one is of more uneven distribution and extension of slipping line,higher stress near the GB,discontinuous and waved propagation of slipping line,more holes and cracks whose locations are much closer to or near the slipping line.