Selective extraction of low-concentration thorium (Th(IV)) from wastewater is a very important research topic. In this paper, amidoxime cellulose was synthesized, and its composition and structure were characterized by FT-IR, SEM, XPS, and elemental analysis. The adsorption experiment results showed that the adsorption reaction was a spontaneous exothermic process. When the solid–liquid ratio was 0.12 g/L and the pH value was 3.5, the adsorption percentage of the Th(IV) in water onto amidoxime-functionalized cellulose (AO-CELL) could reach over 80%. The maximum adsorption capacity can reach to 450 mg/g. At the same time, the adsorption selectivity, desorption process and reusability of the material were also studied. The results showed that the AO-CELL had a good selectivity for Th(IV) in the system with Sr²⁺, Cu²⁺, Mg²⁺, Zn²⁺, Pb²⁺, Ni²⁺, and Co²⁺ as co-ions. In the nitric acid concentration of 0.06 mol/L system, the AO-CELL desorption rate of Th(IV) can reach 95%, and the adsorption rate of Th(IV) in aqueous solution of AO-CELL is still above 60% when the AO-CELL is reused four times. The above results show that the amidoxime cellulose adsorption material synthesized by our research group has good selective adsorption performance for Th(IV) of a low concentration in an aqueous solution and has a good practical application value.