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As an artificial cement based material, cemented tailings backfill (CTB) has significant loading rate (LR)effect, and its deformation and failure are closely related to acoustic emission(AE)characteristics. To study the mesoscopic AE characteristics of the backfill under different LRs, a series of uniaxial compressive strength (UCS) tests with different LRs were carried out for CTB The strength evolution law was determined. With the aid of Particle Flow Code(PFC2D), the crack evolution and mesoscopic AE characteristics of the backfill were analyzed from the mesoscopic point of view. Combined with the theory of energy conservation, the LR effect of the backfill was discussed. The results show that: 1) The uniaxial compressive strength of backfill was positively correlated with the LR, and the relationship between them was a quadratic polynomial function. 2) The numerical simulation results showed that increasing the LR increased the crack initiation stress of the backfill, advanced the crack initiation time and increased the total number of cracks after failure. In addition, with the increase of the LR, the failure mode of the backfill gradually changed from shear failure to tension shear mixed failure. 3)The mesoscopic AE event time step curve experienced initial period, calm period, slow rise period, rapid rise period and rapid decline period, which was highly consistent with the AE characteristics obtained from the test. There were few AE events before the peak, and the AE event dense zone was not obvious. After the peak, AE events and AE events with larger magnitude increase rapidly, forming interconnected AE dense zone. 4) The boundary energy, strain energy and dissipation energy were positively correlated with the LR. The higher LR had a certain blocking effect on the crack initiation and propagation of the backfill, which increased the energy storage limit of the sample, and then improved the strength performance of the backfill. However, the higher energy accumulation before the peak will also lead to the rapid release of energy in the post peak stage, the rapid propagation of cracks, the formation of large mesoscopic damage and the increase of the cumulative number of cracks in the sample. The results can provide reference for the study of the LR effect and mesoscopic AE characteristics of the backfill. [ABSTRACT FROM AUTHOR]