One of the critical techniques for developing hydrogen storage applications is the advanced research to build novel two-dimensional materials with significant capacity and effective reversibility. In this work, we perform first-principles unbiased structure search simulations to find a novel AsC5monolayer with a variety of functionally advantageous characteristics. Based on theoretical simulations, the proposed AsC5has been found to be energetically, dynamically, and thermally stable, supporting the viability of experiment. Since the coupling between H2molecules and the AsC5monolayer is quite weak due to physisorption, it is crucial to be enhanced by thoughtful material design. Hydrogen storage capacity can be greatly enhanced by decorating the AsC5monolayer with Li atoms. Each Li atom on the AsC5substrate is shown to be capable of adsorbing up to four H2molecules with an advantageous average adsorption energy (Ead) of 0.19 eV/H2. The gravimetric density for hydrogen storage adsorption with 16Li and 64 H2of a Li-decorated AsC5monolayer is about 9.7 wt%, which is helpful for the possible application in hydrogen storage. It is discovered that the desorption temperature (TD) is much greater than the hydrogen critical point. Therefore, such crucial characteristics make AsC5-Li be a promising candidate for the experimental setup of hydrogen storage.