Anodic materials with fast kinetics and high capacity are prerequisites for improvement of calcium-ion batteries (CIBs). According to first-principles computations, unique calcium capacity was discovered for B3O3 monolayer. Based on findings, Ca atoms can be adsorbed on B3O3 surface, and the most stable location is the top of the pore center of B3O3 monolayer. Binding energy of B3O3 monolayer is relatively high for Ca atoms. In addition, Ca atoms have been shown to more simple diffuse on B3O3 surface, and lowest diffusion barrier was 65 meV. A more significant finding is that B3O3 monolayer-based nanostructures possess a relatively large capacity of 616.05 mAh/g (as Ca.51BO). These results are expected to support illumination mechanism of Ca storage in boron oxide materials with low-dimensional structures and pave the way for design of CIBs. Therefore, we can utilize the B3O3 anode-based CIBs as alternatives to normal Ca-ion batteries.