According to the empirical electron theory (EET) of solid and molecule, the valence electron structure and theoretical bond energy of C11b-MoSi2 were calculated by the bond length difference (BLD) method. The effects of partial substitution of Al for Si of MoSi2 lattices were considered. According to the average atom model in substitutional solid solutions of EET, the valence electron structure and theoretical bond energy of C11b Mo(Si0.95,Al0.05)2 were analyzed and calculated. The results show that the hybridization state of Mo and Si atoms is altered with Al addition in MoSi2, and then the parameters of valence electron structure change. Compared with MoSi2, the proportion of covalent electrons in total valence electrons decreases from 65.87% to 64.28% and therefore it is concluded that the strength of MoSi2 can be reduced by microalloying with aluminum. However, the lattice electrons increase from 4.7141 to 4.9202, so the plasticity of MoSi2 can be improved by microalloying with aluminum.