Abstract: Cemented paste backfill (CPB) performance is the result of the synergy between different particles and components in the system. It is of great significance to explore the evolution process of the meso-structure of the filling slurry under the action of mixing, which improves the backfill performance and achieves cost reduction in the mines. In this study,Particle Video Microscope (PVM) technology was used to obtain some meso-structure images of the CPB at different mixing times. Then the images were binarized,and the equivalent diameter (d) of aggregate in the slurry was obtained using Avizo software to characterize the meso-structure characteristics of the CPB. Based on the Blake-Kozeny equation and the Hattori-Izumi theory,a d-t relationship model was constructed,and finally,the obtained experimental and theoretical values were compared and analyzed. The results show that the preparation process of CPB is divided into two stages:granule nucleation and shearing dispersion. Under the action of mixing,the equivalent diameter of the aggregate in the slurry increases first and then decreases,and finally tends to be stable. In the granule nucleation stage,a similar "nuclear-shell" structure is formed between particles and liquids,and surrounding particles are continuously adsorbed under the action of liquid bridge force. As more and more particles are adsorbed,the size of the "nuclear-shell" structure gradually increases (The equivalent diameter is proportional to the 0.5 power of time) and reaches a peak around 35 s. In the shearing dispersion stage,the "nuclear-shell" structure cannot adsorb more particles due to its critical volume concentration. The agglomerates break under the action of shearing force,and the meso-structure size becomes smaller and smaller (The equivalent diameter is inversely proportional to time),and tends to be stable after 300 s. The material is transformed into a homogeneous paste state. The meso-structural evolution model based on the equivalent diameter quantifies the backfill material preparation process, and the research results promote the improvement of solid waste backfill technology.