Abstract: Superabsorbent polymers (SAP) are widely used in hygiene, medical, food, agricultural, and environmental fields due to their excellent water absorption and retention properties. However, conventional petroleum-based SAP is difficult to degrade and non-renewable, which has driven the development of cellulose-based alternatives. This paper systematically reviews the research progress of cellulose-based superabsorbent composites. Emphasis is placed on comparing the regulatory mechanisms of different pretreatment techniques on cellulose reactivity, summarizing three major preparation strategies—chemical grafting, surface modification, and composite modification—and elucidating the structure–property relationships among preparation process, network structure, and water absorption/retention/salt tolerance. The functional performance and technical bottlenecks in personal hygiene products, medical dressings, agricultural water retention, and water treatment are discussed. On this basis, challenges such as the inherent trade-off between water absorption and salt tolerance, process complexity, and insufficient application adaptability are identified. Future directions, including green pretreatment, precise structural regulation, and multifunctional synergistic design, are proposed to advance the high-performance and industrial application of cellulose-based superabsorbent composites.