The orientation distribution of chain segments in a uniaxially deformed polymer film has been estimated theoretically as a function of draw ratio using a lattice model similar to the one proposed by Erman et al. The model of Erman et al. was somewhat modified to compare the theoretical results with experimental ones. In doing so, the preferred axis associated with the orientation of segments was chosen along the direction between the two successive cross-link points, and the orientation of the preferred axis was assumed to behave in an affine fashion under elongation. The treatment was formulated in terms of the orientation distribution function with respect to the stretching direction by the application of the Legendre addition theorem. Numerical calculations were carried out to study the mechanism of the orientation of amorphous chain segments of poly(ethylene terephthalate) (PET) films, as well as oriented crystallization of polyethylene (PE) films. X-ray diffraction measurements were done to obtain the orientation distribution functions for PET and PE drawn films. The calculated orientation distribution functions were in good agreement with those observed experimentally.