The cavity tuning characteristics of orthogonally polarized dual-frequency He-Ne laser at 1.15 \mu m are presented. Vectorial-extension model based on semi-classical laser theory reveals that cavity tuning characteristics are related to beat frequency, relative excitation, and type of Ne isotope. Distortions of cavity tuning curves become moderate with the increase of beat frequency because of the weakening of the crosssaturation effect. Distortions are enhanced with the increase of relative excitation because of the combined action of the self-saturation and cross-saturation effects. By adopting dual-isotope Ne instead of monoisotoplic Ne, distortions are reduced because of the misalignment between peaks of the self-saturation and net gain coefficients. The theoretical calculations are in good agreement with the corresponding experimental results.