Ultrahigh molecular weight polyethylene (UHMWPE) fibers have an ultralow interfacial property because of their extraordinarily smooth and nonpolar surfaces, and this property is a persistent problem in UHMWPE fiber-reinforced composites. In this investigation, a novel one-step and mild strategy for enhancing the interfacial property of UHMWPE fiber-reinforced composites was reported. In this strategy, a biomimetic layer with abundant stacked and three-dimensional nanoparticles formed on fibers surface through the synergistic effect of polydopamine and 3-aminopropyltriethoxysilane. Owing to the unique three-dimensional structure and sufficient polar groups on the fibers surface, surface roughness and surface energy significantly increased, and wettability improved. Consequently, the interfacial shear strength (IFSS) of the fibers exhibited a 407.8% increase (8.36 MPa) relative to that of untreated UHMWPE (2.05 MPa) because of these synergistic effects. Further analysis indicated that the failure mechanism of the fibers with the highest IFSS was the transformation from adhesive failure to cohesive failure and substrate failure. The mild preparation process maintained the high crystallinity and orientation of the modified UHMWPE fibers, which exhibited a high tensile force of up to 81 cN.