Compensation of polarization-variance-related artifacts is required to steadily obtain high-quality optical coherence tomography (OCT) images at various experimental conditions. Since most OCT systems utilize optical fiber to transfer the light easily and a polarized light source, the polarization state is arbitrarily changed in every different condition. In this study, we proposed polarization-maintaining-fiber-based polarization-insensitive OCT (PM-PI-OCT) with a simple optical configuration and a simple compensation process. The proposed PM-PI-OCT is not only theoretically proved by mathematical derivations but also evaluated by quantitative analysis of various fiber twisting angles. Moreover, the applicability and robustness of the proposed PM-PI-OCT were proved by human retina imaging using the customized handheld probe. Our proposed polarization-insensitive OCT requires no pre-calibration, no post-processing procedure, and no computational load for implementation and is able to be applied to universal fiber-based OCT systems. We believe that our simple and robust polarization-insensitive OCT system is able to be applied to various existing OCT setups for polarization state variance compensation with high versatility and applicability.