Polarization-sensitive optical coherence tomography (PS-OCT) is a functional imaging technique for biological birefringence tissues. The information contained in the biological tissue can be extracted by analyzing the phase delay. Herein, the influence of polarization state of single incident light on the phase delay accuracy caused by tissue birefringence is analyzed. Initially, the theoretical model is proposed. Subsequently, simulations using MATLAB are performed and finally the theoretical model is verified by experimental measurements. Results obtained by MATLAB along with experimental results show that, when a sample with a fixed amount of phase retardation and a fixed direction of optical axis, and when the orientation is 0° and 90° for the incident linearly polarized light or 45° for the incident elliptically polarized light, the phase retardation measurement error has the smallest value.