The discharge of large amounts of dye-containing wastewater seriously threats the environment. Adsorbents have been adopted to remove these dyes present in the wastewater. However, the high adsorption capacity, predominant pH-responsibility, and excellent recyclability are three challenges to the development of efficient adsorbents. The poly(acryloxyethyl trimethylammonium chloride)-graft-dialdehyde cellulose nanocrystals were synthesized in our work. Subsequently, the cationic dialdehyde cellulose nanocrystal cross-linked chitosan nanocomposite foam was fabricated via freeze-drying of the hydrogel. Under the optimal ratio of the cationic dialdehyde cellulose nanocrystal/chitosan (w/w) of 12/100, the resultant foam (Foam-12) possesses excellent absorption properties, such as high porosity, high content of active sites, strong acid resistance, and high amorphous region. Then, Foam-12 was applied as an eco-friendly adsorbent to remove acid red 134 (a representative of anionic dyes) from aqueous solutions. The maximum dye adsorption capacity of 1238.1 mg∙g^‒1 is achieved under the conditions of 20 mg∙L^‒1 adsorbents, 100 mg∙L^‒1 dye, pH 3.5, 24 h, and 25 °C. The dominant adsorption mechanism for the anionic dye adsorption is electrostatic attraction, and Foam-12 can effectively adsorb acid red 134 at pH 2.5–5.5 and be desorbed at pH 8. Its easy recovery and good reusability are verified by the repeated acid adsorption–alkaline desorption experiments.