Intraparticle diffusion inside porous pellets plays a controlling step in most reactive transport processes. In order to investigate microscopic diffusion process in porous pellets with macro-mesopore structure, a three-dimensional lattice Boltzmann method (LBM) approach with multi-relaxation-time (MRT) collision operator was utilized to calculate the intraparticle diffusivity. With respect to the hierarchical pore structure, the modified random generation of macro-meso pores (RGMMP) algorithm was proposed to obtain pore structure of porous pellets. In this work, a resin catalyst that has macro-mesopore structure was selected as a validation example. Based on the LBM approach, the effects of four geometrical parameters of the modified RGMMP algorithm on the intraparticle diffusivity, namely the total porosity, the ratio of mesopore porosity to macropore porosity, the ratio of average macropore diameter to mesopore diameter and the macropore growth direction were investigated, so as to elucidate the mass transfer mechanism in porous pellets with macro-mesopore structure. These theoretical findings are useful for the pore structure optimization design of porous pellets with macro-mesopore structure. (C) 2019 Elsevier Ltd. All rights reserved.