Abstract: In order to study the failure mechanism of weakly bonded rock beam in the re-mining roof structure, based on the model of re-mining roof, the numerical model of the weakly bonded rock beam is built by the discrete element software 3DEC. The instability process of the rock beam in the weakly consolidated compaction zone is simulated and analyzed. The results show that the weak cemented rock beam generally first forms three-hinged rock arch structure before the instability; with the increase of plastic deformation of the hinged point, the stability of the three hinged arch decreases and the cracks and slippages of the rock mass cement surface appear to lead to the collapse of the whole rock beam; the smaller the span of the rock blocks, the lower the stability of the roof; when the number of exposed blocks is more than 2 and even number, the joints are only cracked at three hinged points. The hinged points of the two boundaries are “V” shape and the middle hinged point is “inverted V” shape.