Straight lines drawn on a film were deformed into parabolic ones after passing through the annealing zone of a tenter. It became theoretically evident that shear stress acted backward along the film in proportion to the distance from the center to the edge. The optical anisotropy, which was generated in the tenter and depended on the position on the film, was calculated, assuming that the refractive index ellipsoids were deformed in proportion to the shear stress. The results follow: 1. The refractive index ellipsoid of the film is not deformed at the center of film. 2. The birefringence patterns (birefringence∼transverse position) are downward convex and had a minimum near the center of the films. 3. The birefringence increases in proportion to the distance from the center to the edge, when the initial birefringence is zero. 4. The planar orientation is unaffected by heat-setting at any location in the films. 5. The angle of γ is 90° at the center of the film and decreases from the center to the edge, when the initial γ direction is pararell to the machine direction. 6. The angle of γ is 0° at the center of the film and increases from the center to the edge, when the initial γ direction is perpendiculer to the machine direction.