On the basis of the Michelson interferometer, a phase interference measurement system with one single arm as the measurement output port was designed to measure and analyze the thickness uniformity of a glass plate. In the system, a CCD camera was used to collect the interference pattern and the Fourier transform fringe analysis and phase unwrapping techniques were used to extracted the phase information contained in the interference pattern. For the problem that the sidelobe center of Fourier transform spectrum could not be accurately located, an applicable triangular transformation method was proposed to extract the volume of phase change directly. With this approach, the phase results could be obtained more accurately without knowing the central location of the spectral sidelobe, meanwhile, the errors induced by man-made estimation and the small carrier frequency component in vertical axis were eliminated. The thickness uniformity of a group of glass plates was measured in both of the length and width directions. The experimental results show that the theoretical accuracy is 0.93% and 0.92% in two directions, respectively, when they measured by a CCD camera with a unit size of 4.65 μm×4.65 μm. The system can measure the thickness uniformity of the glass plates, and has lower demands for the location accuracy of frequency spectral sidelobe and the direction precision of carrier frequency.