Abstract: In order to study the influence of different crystal particle sizes on the acoustic emission calm period of rocks，a granite equivalent crystal model GBM （Grain-based model，GBM） numerical calculation model was constructed based on the particle flow code PFC2D. The microscopic parameters were calibrated through laboratory test results， which simulates the uniaxial compression acoustic emission test of granite specimens. The influence law of different crystal particle sizes on stress-strain and peak strength of specimens was analyzed. And the spatial and temporal evolution characteristics of cracks， acoustic emission events and the generation of relative quiet period during the failure process of specimens were emphatically analyzed. At the same time， the energy variation characteristics of before and after acoustic emission quiet period of specimens and the relationship between the energy variation and the crystal particle size were studied. The results show that: ①With the increase of crystal size， the uniaxial compressive strength of specimens increases. The failure forms of the specimens were mainly X-shear and V-columnar splitting. At the same time， the specimens with different crystal particle sizes were mainly damaged by tension， and the intergranular microcracks first occurred， and the transgranular microcracks began to occur at the starting point of acoustic emission quiet period.② In the uniaxial compression process of specimens， acoustic emission appears relative calm periods of varying degrees before the stress peak. In addition， the location of acoustic emission generation before the quiet period is along the crystal boundary， and after the beginning point of the quiet period， acoustic emission located in the crystal interior and the crystal boundary will be generated simultaneously.③ The variation of slip energy and damping energy decreases with the increase of crystal particle size in the acoustic emission quiet period.Among them，due to the significant decrease of acoustic emission during the quiet period of acoustic emission，the activity inside the rock is in a relatively calm state，so the released kinetic energy is reduced.

Key words: acoustic emission, equivalent crystal, PFC, relative calm period, granite