In order to reveal the micromechanical nature of deep rock failure and obtain the precursory information of rock failure, based on the force chain research and the discrete element theory of discontinuous media, the quantitative characterization of rock micromechanical characteristics and acoustic emission were carried out by PFC numerical simulation method. The results show that: the change of coordination number between particles indicates the change of bonding number between particles, which further characterizes the development of microcracks, and the coordination number of particles is negatively correlated with the overall development of cracks; In the process of rock loading, the "strong chain" is formed near the macro failure surface, and its extension direction gradually deflects to the macro failure surface direction, and finally is consistent with the macro failure surface direction; The acoustic emission simulation research method is improved. The acoustic emission evolution process is divided into five stages, and the spatial distribution characteristics of acoustic emission are proved. Acoustic emission events are mainly concentrated near the macro failure surface of rock, which quantitatively characterizes the intensity of acoustic emission. There is a short silence period of acoustic emission before the peak value of rock, and this characteristic is defined as the "critical precursory information" of rock failure.