Glass is the basis of industrial raw materials, and the improvement of its output and quality plays an important role in practical application. How to measure the thickness of glass at high speed and accurately has become an urgent problem to be solved in glass production line. Among many measuring methods, laser ranging has the advantages of high precision, fast speed, non-contact and convenient operation. In this paper, the distance between the laser emitter and the front and rear surfaces of the glass parts to be measured is measured by laser frequency sweep interferometry ranging system, and the thickness of the glass parts to be measured is obtained by calculating the distance difference. Firstly, the beat signal of the distance is obtained, and the beat signal is compensated by interpolation fitting method to realize nonlinear correction. By interpolating the beat signal after nonlinear correction, the number of measured signal points after interpolation is 20 times that before interpolation, and the phase signal becomes smooth. Then, the phase extreme point is selected for phase splicing to increase the number of signal measurements and reduce the influence of spectrum leakage on the experimental results. Finally, the splicing signal is performed by fast Fourier transform to obtain the distance difference between the front and rear surfaces of the glass to be measured, namely the thickness of the glass. The experimental results show that the thickness error of glass without phase splicing treatment is less than 50 μm, and the thickness error of glass with phase splicing treatment is less than 15 μm. The phase splicing method effectively improves the precision of glass thickness measurement in industry.