Calcium aluminate cements (CACs) have attracted much attention due to their potential applications in severe environments. Up to now, their structural, electronic, and mechanical properties have not been fully determined yet. This study shed light on these properties by means of first-principles density functional theory. A total of ten phases, including C3A, C12A7, CA (CA_low, CA_A, and CA_B), CA2, CA6, C2A, C5A3 and C4A3, within the calcium aluminate (Ca-Al-O) series were investigated. The calculated lattice parameters agreed well with the experimental results. The cohesive energy was ranged between 5.90 eV/atom and 6.31 eV/atom, and the formation energy was ranged between 14.42 eV/atom and 5.51 eV/atom. The partial density of states that are important for bond formation originated mainly from O atoms, followed by Ca and Al atoms. All ten phases contained band gaps ranged between 3.74 eV and 5.30 eV. Oxygen atoms were prone to electrophilic attack while calcium atoms were prone to nucleophilic attacks. The bulk modulus, shear modulus, Young's modulus, and Poisson's ratio for C3A, C12A7, CA_low, CA6, C2A, C4A3 were in the range of 79.37 GPa to 197.25 GPa, 42.11 GPa to 102.81 GPa, 107.33 GPa to 262.78 GPa, and 0.25 to 0.28, respectively.