Solar-driven interfacial water evaporation technology has garnered significant attention due to its considerable potential in seawater desalination and wastewater treatment. Cellulose-based aerogel (CBA) has become a highly promising photothermal evaporation material due to its excellent hydrophilicity, controllable porous structure, low thermal conductivity, abundant sources, and biodegradability. This chapter systematically discusses the research progress and related applications of CBAs in solar steam evaporation. The core design principles of efficient photothermal evaporators were introduced, encompassing three key aspects: light absorption and photothermal conversion, thermal management optimization, and synergy between water and materials. In addition, various preparation methods for cellulose aerogel (such as freeze-drying and chemical cross-linking) were introduced, and the excellent performance of cellulose aerogel in a photothermal evaporation system was demonstrated through specific examples. Finally, the multi-functional and integrated applications of CBA photothermal evaporation systems beyond sustainable water production are discussed, and the future development of CBAs is prospected. This chapter provides a theoretical reference and basis for the development of high-performance, multi-functional, and environmentally friendly cellulose-based solar water evaporation materials.