Optical birefringence is measured by a high-frequency modulation method using a photoelastic modulator and polarized laser. A modified synthesized method was developed and applied for the measurement of stress distributions of a glass plate. The distributions of the differences of principal stresses and their directions were obtained directly by this method. The stress distributions under tensile load of a pulled rectangular glass plate with a hole at its center were measured. The results of stress distributions agreed with the analytical results. It was confirmed experimentally that the spatial resolution of stress measurement was the same as the diameter of the laser light. The stress at many points could be obtained quickly by the synthesized method and scanning stress distribution measurement was realized.