CaF_2/Si(111) interfaces formed at 700℃ as well as at room temperature have been studied with XPS, UPS and LEED. The experimental results show that the substrate temperature has a significant influence on the interface in respect of ifs electronic structure and chemical bond. When the substrate temperature was at 700℃, the interface is found to be consisted of predominate Si-Ca bonds which correspond to an interface state located at 1.2eV below Fermi level. There is depletion of fluorine atoms due to the dissociation of the CaF2 molecule at the interface. When the substrate was at room temperature, there are no chemical bonds between substrate and adatoms nor depletion of fluorine atoms at the interface. Annealing of this interface at 700℃ results in preferential evaporation of F, and the surface undergoes a number of reconstructions until a 3×1 reconstruction is obtained. The bonding at this interface is similar to that of CaF2/Si(111) interface when the substrate temperature was at 700℃. The experimental results show that the substrate temperature has a significant influence on the interface in respect of ifs electronic structure and chemical bond. When the substrate temperature was at 700 ° C, the interface is found to be consisted of predominate Si-Ca bonds which correspond to an interface state located at 1.2eV below Fermi level. There is depletion of fluorine atoms due to the dissociation of the CaF2 molecule at the interface. When the substrate was at room temperature, there are no chemical bonds between the substrate and adatoms nor depletion of fluorine atoms at the interface. Annealing of this interface at 700 ° C results in preferential evaporation of F, and the surface undergoes a number of reconstructions until a 3 × 1 reconstruction is obtained. The bonding at this interface is similar to that of CaF2 / Si (111) interface when the substrate temperature w as at 700 ℃.