In the case of measurement of Li Kα using by electron beam excitation, it was found that the detection of Li Kα of insulator compound, except LiF, was so difficult while the measurement of metallic Li was so easy. For this point, the examination with cluster calculation was carried out. From the results of the calculation, it was revealed that the detected Li Kα of LiF in our measurement was not original of LiF, but the Li which was reduced and changed to metallic state by the primary electron beam irradiation. And, the result of the calculation suggested that the conduction electron might be contribute to the dipole transition process and the generation of Kα, while the all of other valence electrons mainly relax to core level by Auger decay process.