Abstract: To explore the effects of cellulose nanocrystals (CNC) and coated CNC polyethylene (PE) fibers on the performance of mortar, XRD was employed to analyze the hydration products, and nuclear magnetic resonance (NMR) technique was taken to measure porosity. Calcium-silicon ratio of calcium silicate hydrate (C-S-H) was measured by EDS and PE/C-S-H interface was characterized by SEM. The adsorption energies, kinetic properties and gyration of radius between the two CNCs and C-S-H were analyzed by molecular dynamics simulations (MD). The needle-like CNC promotes hydration and affects the compactness of the hydration products, curbs the development of pores and improves the mechanical properties of the mortar. There are differences in the adsorption between different functional groups and cement matrix, which affects the reinforcement effect of cellulose nanocrystals. CNC coating improves the bonding between the fibers and the cement matrix, improving the synergistic performance of composite materials.