Based on the classical theory of surface diffusion and evaporation-condensation along with its weak statement,a finite element program is developed for simulating the evolution of intergranular microcracks in Copper due to surface diffusion induced by stress migration. The results show that there exists critical values of the stress and the aspect ratiofor the intergranular microcrack under the biaxial tensile stress. When the stress or the aspect ratio is less than the critical values,the microcrack will directly evolve into a cylinder. When the stress or the aspect ratio is equal or greater than the critical values,it will grow and split into three small microcracks along the grain boundary. The splitting time of the intergranular microcrack reduces with increasing the stress or the aspect ratio,which means that the increase of the stress and the aspect ratio will accelerate the splitting process. The critical values of the stress and the aspect ratio decrease when the tress and the aspect ratio increase,that is,the increases of the stress and the aspect ratio are beneficial to the microcrack splitting. In addition,the higher of the ratio between the grain-boundary energy and the surface energy,the shorter of the splitting time will be.%基于表面扩散和蒸发-凝结的经典理论及其弱解描述，对应力诱发表面扩散下铜内沿晶微裂纹演化进行了有限元分析。结果表明：沿晶微裂纹演化分节存在临界外载和临界形态比，当外载或形态比小于临界值时，微裂纹逐渐圆柱化；当外载或形态比大于等于临界值时，微裂纹沿晶界方向扩展并分节为三个裂腔。微裂纹分节时间随外载的增大和形态比的增大都减小，即外载和形态比的增大加速微裂纹分节。而临界外载和临界形态比随着形态比或外载的增大而减小，表明形态比和外载的增大都将有助于微裂纹分节。此外，沿晶微裂纹中晶界能与表面能比值的增大会加快微裂纹的分节。
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