Before rock failure, it is found that ae distributed densely, and the coming fracture will occur in the density center of high magnitude events, and ae ratio of frequency grows greatly . these precursors can be presented by the change of b value, a t value and the contour of v value . prefab crack systems in the specimen will affect the fractures hi rocks 关于岩石破裂过程中一些物理量的变化,发现在岩石破裂前,主破裂发生的区域先出现大能级声发射的密集分布;在岩石加载的临界状态,大能级的声发射数量大量增加;在接近临界时,大能级声发射事件在失稳前频度突然加快。