The geometries, stabilities, and spectral properties of Ca2Sin(n=1~9) clusters are systematically investigated by using first principles calculations based on the hybrid density functional theory at the B3LYP / 6-311G (d) level. The optimized geometries indicate that the most stable structures of Ca2Sin clusters are three-dimensional structures for n=3~9. On the basis of the obtained lowest-energy geometries, the size dependence of cluster properties, such as averaged binding energies, second-order energy differences, fragmentation energies, HOMO-LUMO gaps and spectral properties, are discussed. The calculated results show that the impurity Ca atoms in the Ca2Sin clusters enhance the chemical stability of the silicon framework. The magic clusters are found at n=5, 7 and 9. In addition, the spectral analysis indicates, the number of the infrared (IR) absorption peaks of Ca2Si5 and Ca2Si9 is more, but Ca2Si7 is less. The Raman absorption peak of Ca2Si5 is only one and appears in the low frequency band, on the contray, Ca2Si7 and Ca2Si9 have more Raman absorption peaks.