Using classical vibrator theory and by means of the n-k egg-shape curve and n-k half-circle graph of reflectivity for vibrators, the influence of high-frequency dielectric constant on crystal reflection spectrum is analyzed. It is pointed out that the materials, of which the high-frequency dielectric constants are small, are advantageous to the formation of a wide low-reflectivity region in their reflection spectrum when their damping constants and oscillator strength are constant. Thus they can serve as infrared wave-absorbing material.