Stress-induced migration near the grain boundary in Al thin interconnect is studied by means of an ab initio molecular dynamics simulation formulated on the basis of the effective-medium theory. The consistent grain boundary model is used, whose geometry is characterized by Σ-value. It is shown that besides Σ-value, existence of high-energy sites near the grain-boundary is an important factor which promotes nucleation and growth of voids. In the bulk state, grain boundary decohesion due to coalescence of voids is dominant in the high-boundary-energy case, and growth of a small number of voids leads to breakage of the Al wire with the grain boundary of low energy and high consistency. If there exists a free surface, marked decrease in thickness near the grain boundary occurs and a narrow groove develops in the high-energy case.