Abstract: Uranium mining and hydrometallurgy produce a large amount of uranium wastewater, which causes pollution to the surrounding ecological environment. Therefore, efficient and green treatment is an important basis to guarantee the sustainable development and ecological security of nuclear industry. In this study, sunflower leaves were used as raw materials for green synthesis of biochar-loaded nano-iron particles (GN-FeNPs/BC) that used to remove U(VI) in water. Sunflower leaves were used to prepare plant extract, and then the residue was pyrolyzed to prepare biochar. Finally, ferrous sulfate heptahydrate solution, biochar and plant extract were mixed to successfully prepare a green nano-iron composite material. The effects of biochar carbonization temperature, iron-to-carbon ratio, pH value, temperature, time and U(VI) concentration on uranium removal were explored. When the pH is 5 at 298 K, the maximum adsorption capacity is 96.43 mg·g⁻¹. The kinetics and thermodynamics are studied. The results show that the pseudo-second order model and Langmuir model fit well. The thermodynamic constants indicate that the adsorption of U(VI) by GN-FeNPs/BC is a spontaneous endothermic process. XPS analysis shows that the removal mechanism includes adsorption and reduction.