4 kinds of conventional polarization maintaining (PM) fibers and one sort of novel PM photonic crystal fiber (PCF) are evaluated to understand their polarization maintaining (PM) abilities at a condition of working temperature changing. These fibers are widely used in fiber sensing application, such as fiber optical gyros (FOG), electronic current meters and so forth. Using Optical Coherence Domain Polarimeter (OCDP), we carried out high precision experiments to test fiber's birefringence. It proposed a direct application reference for fiber sensing, especially to fiber optical gyros, in which polarization of light should be considered strongly.