Binders are needed for the pelletization of zeolite catalysts, and the pore network structure of binders can significantly affect the catalytic performance of zeolite catalyst pellets. In this work, a multiscale model directly coupling model equations at crystal, pellet, and reactor levels is proposed to engineer the pore network structure of binders. Benzene alkylation with ethylene catalyzed by ZSM-5 zeolite pellets in a fixed-bed reactor is taken as the model reaction system. The results show that strong diffusion limitations exist in crystals (micropores) and binders (macro-/mesopores). Shrinking the crystal size or adding intracrystalline pores in crystals can reduce the diffusion limitation in micropores but also can enhance the diffusion limitations in macro-/mesopores. An optimal volume fraction of binders can balance diffusion in binders and reaction in crystals and thus results in a maximum conversion of ethylene. The zeolite pellet with a higher binder porosity and a larger binder pore diameter is more favorable, and the influence of binder porosity is stronger than that of the binder pore diameter. In addition, crystallizing the binder into the zeolite phase can largely enhance the catalytic performance of zeolite catalyst pellets, especially when the volume fraction and porosity of the binder are high. This work gives a multiscale model and some useful guidance for developing zeolite catalyst pellets used in industry.