The rapid development of electric vehicles has promoted researchers to explore the field of high-capacity batteries. Two-dimensional (2D) materials have been proven to have ultra-high storage capacity due to their unique structural advantages. A first-principles approach was applied here to verify the feasibility of the novel AlB2 monolayer as an anode material with ultra-high storage capacity for Li/Na-ion batteries. The Li capacity of AlB2 monolayer is up to 3308.6 mAh/g. Meanwhile, the Na capacity up to 1654.3 mAh/g. It is worth noting that the diffusion barrier of the monolayer is extremely low (Li: 0.50 eV; Na 0.26 eV). The results show that AlB2 monolayer is a kind of anode material for high energy storage, which provides a new choice for the development of long-life battery.