The mesoscopic structure of rocks determines their strength and deformation characteristics. The grain and pore size distribution of granite samples buried depth of 1600 m to 1900 m in a goldmine of Shandong Province are measured by polarizing microscope and low-field nuclear magnetic resonance. The splitting test is carried out and the acoustic emission signal is obtained in real time by using an electro-hydraulic servo press and PCI-2 acoustic emission collector. The relationship between meso-mechanics and acoustic emission characteristics of split granite is analyzed. The experimental result shows that there is no clear correlation between meso-grain size and pore size distribution. Rocks with larger mineral grains easily form inter-embedded structures between grains and grains, the bearing effect of grains is enhanced, and the tensile strength of rocks is improved. The level of stress concentration in the rock is closely related to the pore size of the rock, and the acoustic emission ringing count before the main rupture in the large aperture (0.1~10 mm) of the rock is more active than that of the small aperture rock (0.01~1 mm), and a large number of high frequency acoustic signals are induced by the penetration between the pores in the unstable failure stage and post-peak failure stage, the stress concentration is higher, and the energy release frequency is increased, however the energy released strength by a fracture is weak.