Abstract: To solve the superposition problem of stress birefringence in measuring stress birefringence of optical glass, using optical equivalence principle, the superposition model was replaced by a system containing a birefringent plate and a rotator. The superposition of stress birefringence analyzed and calculated. Curves of phase retardation, azimuth of the principal axis of birefringent model, and rotation angle of the rotator changing with the angle between two azimuths of principal axis of the birefringent model were obtained. Results indicate that the superposition of stress birefringence is not a simple sum of it, it is related to the magnitude of birefringence and the angle of stress of each superposition model. The stress birefringence measurement value matches the theoretical value. The superposition of stress birefringence influences optical glass measurement adversely, reducing the measurement precision, especially when transparent support or refractive liquid containers exist, the influence of superposition of stress birefringence cannot be ignored.