The simultaneous high-capacity and fast removal of radioactive barium ion (Ba²⁺) from nuclear wastewater is necessary but still faces large challenge. In this study, a novel adsorbent containing sulfonic group, MOF-808-SO₃H, was prepared based on the oxidation of –SH group. Characterizations confirm the successful introduction of –SO₃H, good porosity, and stability of the material. The adsorbent exhibits excellent capture ability for Ba²⁺ due to strong hard acid-base and electrostatic interactions, with the adsorption capacity of 152.0 mg g⁻¹ and fast equilibrium adsorption time, superior to other reported materials. Optimal pH was found to be almost neutral and temperature cannot affect the adsorption largely. Besides, the irreversible adsorption was demonstrated and thereby the secondary pollution may be avoided. Therefore, our work provides an efficient adsorbent for capturing Ba²⁺ irreversibly, and proposes a feasible strategy for constructing adsorbents with simultaneous high adsorption capacity and fast kinetics.