Multi-beam laser heterodyne measurement of glass thiclcness is based on laser heterodyne measurement technology and laser Doppler technology. We deduced the harmonic expression of photodetector output current, discussed the feasibility and theory of the method which make use of the non-contact multi-beam laser heterodyne to increase the precision of the glass thickness measurement, and made simulation in different situation with Matlab. The results showed that the maximum error is 0.3% at different incidence angles in flat glass thickness measurement, which has an obvious advantage in accuracy over the other methods.