Abstract: This paper gives a brief overview of the advances in the research of crack, dislocation, grain boundary and their interactions by molecular dynamics method. The contents include:dislocation nucleation and emission from crack tip; the unstable stacking criterion for the dislocation emission from crack tip; the effect of crack and crystal geometry on the dislocation emission; tem-perature dependent dislocation nucleation and emission processes; and the in-teraction of an array of dislocations emitted from cra...