Flat glass is widely used in construction,transportation,aerospace and other fields,and its stress is an important index to measure product quality.In order to detect the small stress in glass quickly and accurately,this paper studies the technology for testing stress of flat glass based on laser feedback effect.By discussing the phenomenon of polarization flipping in laser feedback theory,the problem of measuring lock area in the system is analyzed,and the method of adding offset wave plate is adopted to expand the measuring range of the system.The accuracy and repeatability of the detection technology are improved after excluding the errors caused by external temperature by analyzing the error of the measurement results of the sample.The experimental results show that the maximum value of the sample of flat glass is 0.65 Mpa,and the standard deviation is less than 0.15 Mpa,which belongs to the standard stress range of the product.In addition,the testing system has the characteristics of simple structure,high accuracy and strong stability,which provides an important method for on-line nondestructive testing the stress in flat glass.