A polarization phase-shifting interferometric method is proposed to measure the central stress in flat glass based on the principle of plane polarization interferometry. Rotating analyzer can be used to realize polarization phase-shifting. The stress birefringence values and their distribution curves are obtained with the constructed mathematical model, and then the central stress value can be calculated from the stress-optical coefficients. The central stress of float flat glass is experimentally investigated and the experimental results show that the measurement error of this proposed method is less than 3%, and the measurement repeatability is superior to 1 nm·cm -1, which can verify the feasibility of this proposed method.