In this paper, We propose a novel method of measuring glass thickness by means of multi-beam laser heterodyne. Based on the Doppler effect and the heterodyne technology, loading the information about the glass thickness into the frequency difference of the multi-beam laser heterodyne signals by sinusoidal frequency modulation of the oscillating mirror that is in a simple harmonic motion, we can simultaneously obtain many values of the glass thickness through the multi-beam laser heterodyne signal demodulation. Processing these values by weighted-average, the glass thickness can be obtained accurately. This novel method is used to simulate the measurements for different glass thicknesses by MATLAB, the obtained result shows that the relative measurement error obtained by using this method is just 0.008%.