Dual optical path transmission method was proposed for the thickness measurement of float glass according to the optical reflection and transmission principles. In this method, two symmetrical line lasers were adopted to irradiate the float glass at the same time, and the two transmitted beams were imaged on the photosensitive unit of the CCD image sensor after reflected by the two reflectors symmetrically located on the other side of the glass. Then Matlab was used to make de-noising processing on the light band image collected by the acquisition card. In order to extract the center pixel of the light band image, the algorithm of gray gravity was adopted after threshold boundary treatment, and the difference between the thickness of the glass and the center pixel is given by analyzing the quantity relationship formula. According to the experiments performed on the glass with different thicknesses, it is indicated that the dual optical path transmission method can realize high-accuracy measurement, meeting the requirements of national standards.