The issue of water pollution is becoming increasingly severe, highlighting the urgent need to develop efficient and sustainable methods for pollutant removal. This study proposed the use of ambient pressure drying to prepare a nanocellulose-based aerogel with high adsorption capacity for both anionic and cationic pollutants. Polyethyleneimine (PEI) was first attached to a carboxymethylated cellulose nanofiber (CNF) framework through electrostatic interactions. Then, γ-aminopropyltriethoxysilane (APTES) and glutaraldehyde (GA) were used for chemical crosslinking to form a hydrogel. Finally, through solvent exchange and ambient pressure drying, a low-density (18.80 mg/cm³) and high-porosity (92.06%) CNF/PEI composite aerogel (CPA) was obtained. This aerogel demonstrated excellent structural stability in water. Owing to the coexistence of anionic carboxymethyl and cationic amino groups, the aerogel exhibited strong adsorption capacity of aerogel per gram for both cationic and anionic dyes in complex wastewater environments. The maximum adsorption capacities of aerogel per gram for methylene blaue (MB) and Congo red (CR) were 516 mg and 2090 mg, respectively, with removal rates of over 98% for both anionic and cationic dyes. In addition, the aerogel exhibited good structural stability and fatigue resistance. After soaking in an alkaline solution for a week, it remained intact, and after 10 cycles of compression in the wet state, its elasticity recovery rate remained at 60%. Compared to similar adsorption materials, CPA shows significant advantages in terms of adsorption capacity, amphoteric adsorption ability, and reusability. The preparation method proposed in this study is time-efficient and highly effective, making it suitable for large-scale production, with promising potential for application in industrial wastewater treatment.