Mixture of high-density bentonite pellets are considered as a potential buffer/backfill material for high-level radioactive wastes (HLW) repository. One of the outstanding problems of this material is the particle segregation induced by vibration during transportation and emplacement. In this work, the vibration-induced segregation behavior of crushed GMZ (Gaomiaozi) bentonite pellet mixtures with different size distributions was experimentally investigated using a cylindrical container under vertical vibrations. The degree of segregation was evaluated by a weighted coefficient of variation (WCV) reflecting the changes in particle size distribution before and after vibration. Results show that generally the WCV increases with decreases of particle size ratio, the mass fraction of the fine size class and the number of size classes of the mixture. The influences of particle size ratio and distribution were interpreted by two dominant mechanisms including percolation and convection, and could be incorporated into a particle characteristic index (PCI). Further analysis shows that the WCV monotonously increases with the increase of PCI and the relationship between them can be well described using a sigmoid function. Finally, based on the analyses of the experimental results, strategies for reducing segregation were proposed.