An optical method to measure micro-stress based on common-path heterodyne interference technology via multiplet total reflections is presented. A heterodyne light beam with two polarization states (s-polarization and p-polarization) is incident on a grating, the first-order diffraction light is generated. Because the grating is stretched by stress, its period changes thus the first-order diffractive angle has offset. Then, the first-order diffraction beam enters a strip prism and total reflection occurs, which cause the variation in phase difference between the s-polarized and the p-polarized light. By substituting the phase difference into the derived grating stress equation, the stress can be calculated. The measurement accuracy can be improved by multiple total reflections inside the prism. According to the simulation results, when the incidence angle is -5°, the grating period is 10 μm, and the number of total reflections is 30, the stress sensitivity to phase is 1.500 N/(°) and the resolution is 0.015 N. This method has such advantages as simple structure, rapid measurement, high sensitivity and free from outside disturbance.