A method based on Mach–Zehnder interferometer and stress optical coefficients theory was proposed for measuring the photoelastic coefficients of optical glasses. The corresponding apparatus is built to measure the photoelastic coefficients of fused silica and As₂S₃ glasses, with p₁₂  =  0.27 and 0.26 at 632.8 nm, respectively. The validity and accuracy of the present technique were tested on the samples of fused silica and As₂S₃ glass, with the relative error not exceeding 10% compared to that in previous studies and the causes of errors were analyzed. The photoelastic coefficients of tellurite glasses with component 75TeO₂-20ZnO-5Na₂O were measured, with p₁₁  =  0.23 and p₁₂  =  0.22. The acousto-optic (AO) figure of merit M₂ of the three types of glass was calculated and the role of photoelastic coefficient in the equation was discussed, providing an effective technique for investigating the AO interaction in a glass.