Coal-gas outburst, rock burst, and other mine dynamic disasters are closely related to the instability and failure of coal-rock. Coal-rock is the assemblies of mineral particles of varying sizes and shapes bonded together by cementing materials. The damage and rupture process of coal-rock is accompanied by acoustic emission (AE), which can be used as an effective means to monitor and predict the instability of coal-rock body. In this manuscript, considering the size effect of coal-rock, the influence of different height to diameter ratio on the acoustic emission characteristics of coal-rock damage evolution was discussed by microparticle flow PFC2D software platform. The results show that coal-rock size influences the uniaxial compressive strength, peak strain, and elastic modulus of itself; the size effect has little effect on the acoustic emission law of coal-rock damage and the effects of the size of coal-rock samples on acoustic emission characteristics are mainly reflected in three aspects: the triggering time of acoustic emission, the strain range of strong acoustic emission, and the intensity of acoustic emission; the damage evolution of coal-rock specimen can be divided into 4 stages: initial damage, stable development, accelerated development, and damage.

In this manuscript, the numerical coal-rock combined bodies with different height ratios of rock part to coal-rock combined body (HRRC) were established by particle flow code (PFC) firstly, and then the influence of different HRRC on mechanical properties and numerical acoustic emission (AE) characteristics of coal-rock combined bodies were investigated. Finally, the damage constitutive model of the coal-rock combined body was discussed. The research results show that with the increase of the HRRC, the UCS and the elastic modulus (E) of the combined coal-rock bodies increased. The failure of coal-rock combined bodies is mainly focused on the coal body. The evolution law of AE hits of coal-rock combined bodies have three stages, named stable stage, rapid ascending stage, and rapid descending stage. The damage variable curves of coal-rock combined body have two stages, named slowly damage stage and sharply damage stage. The damage constitutive relation based on AE hits can well reflect the stress-strain relationships with a lower HRRC. However, for a higher HRRC, the damage constitutive equation is not accurately and the damage of the rock part in the coal-rock-combined body should be considered.