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In this work, we study the performance of hydrogen storage of superalkali cluster OLi3 decorated monolayer hexagonal boron nitride (h-BN) by using first-principles calculations. We find that the O–B bond is strong enough for superalkali cluster OLi3 anchor to the monolayer h-BN substrate with thermodynamic stability at room temperature. The Li atom of monolayer OLi3-decorated h-BN becomes cationic leading to the form of a local electronic field around the Li atom and acts as a binding site to adsorb hydrogen molecules. The monolayer 2(OLi3)-decorated h-BN can adsorb 16 H2 molecules with the maximum average adsorption energy per hydrogen molecule of −0.175 eV, which falls in the ideal window for reversible uptake-release at ambient temperatures. The H2 molecules theory storage gravimetric density of 2(OLi3)-decorated h-BN reaches 9.67 wt. %. The mechanism of H2 molecules adsorbed on monolayer OLi3-decorated h-BN can be attributed to the weak orbital interaction and electrostatic mutual attraction between the H atom and Li atom. The effects of temperature and pressure on the hydrogen storage performance are also investigated, and the results show that the hydrogen adsorbed structures of superalkali cluster OLi3-decorated h-BN monolayer are stable at room temperature under mild pressure. [ABSTRACT FROM AUTHOR]