Abstract: Moisture-induced aging in humid environments remains one of the critical challenges affecting the long-term service performance of fiber-reinforced composites. The diffusion and accumulation of water within composites not only induce plasticization, hydrolysis, and microstructural relaxation of the polymer matrix, but also weaken the fiber-matrix interfacial bonding, thereby leading to pronounced degradation in mechanical properties and service reliability. This review provides a systematic overview of recent advances in moisture-protection technologies for fiber-reinforced composites, with particular emphasis on three major approaches: surface barrier engineering, bulk modification, and self-healing protection. Surface barrier strategies primarily involve the construction of superhydrophobic coatings, nanocomposite barrier layers, or dense thin films prepared by atomic layer deposition on composite surfaces, thereby forming low-permeability physical barriers to effectively suppress water ingress. Bulk modification strategies aim to reduce the intrinsic moisture uptake of composites or enable in situ capture and transport retardation of infiltrated water through the incorporation of solid desiccants, hydrophobic functional groups, or nanofillers. Self-healing protection strategies endow coatings with the capability to autonomously restore barrier integrity after damage, among which intelligent self-healing coatings based on dynamic covalent bonds, microcapsule technologies, and environmentally responsive mechanisms have shown considerable application potential. Furthermore, this review discusses the key challenges facing current moisture-protection technologies, including insufficient long-term durability, interfacial instability, multifunctional integration, and engineering-scale implementation. Finally, future perspectives are proposed with regard to biomimetic moisture-resistant surfaces, structural design of nanomaterials, green and sustainable protective systems, and intelligent moisture-protection platforms.