It is applied to precisely measure flat glass thickness. This instrument is designed with high measurement accuracy, small size, simple operation and convenient to carry. It is mainly composed of measuring head, controller and optical fiber. A specific color-coded lens is used to generate axial dispersion of the white light, and the reflected signal of the measured workpiece is analyzed by the spectrometer to analyze the confocal light wave signal. Finally, the measured displacement of the workpiece is calculated by the wavelength and displacement conversion curve.