Using first-principles method, we studied the electronic structure and the bonding mechanism of La-Ir-Si materials. The results of the band structure and the density of the states indicated that the superconducting property of the La-Ir-Si system is determined by the p-d coupling strength between the transition element Ir-d and Si-p states of the material. In order to quantitatively describe the p-d coupling strength, we calculated the charge transfer during the bond process of the materials using the atom-in-molecule method. The results revealed that the superconducting transition temperature TC is linerly proportional to the atomic basin charges of Ir.