As an aid in establishing an understanding on the electronic level,the influence of bismuth on the cohesion of nickeló5 (012) grain boundary was determined using the plane wave pseudopotential (PWPP) method with the generalized gradient approximation. Based on the Rice-Wang model,the total energy calculations show that Bi behaves as an embrittler of the Ni grain-boundary,which predicts the experimentally known behavior. The total charge density,and difference charge density of the grain boundary also demonstrats that the Bi atom forms weaker bonds with neighboring Ni atoms in the grain boundary region. Total density of states (DOS) show that there exists significant covalent bonding for the grain boundary system with Bi segregated which help to embrittle the grain boundary and the change that Ni local d-DOS is narrowed due to segregation of Bi is also beneficial for the decohesion.