Abstract: Transmission characteristics of a high-birefringence Sagnac loop was studied by using transfer matrix method, numerical simulation and experimental investigation. The Sagnac loop filter was composed of an optical coupler (OC), a polarization controller (PC) and polarization-maintaining fiber (PMF). The influence of PMF characteristics and PC state on transmission characteristics of Sagnac loop was theoretically analyzed. The transmission spectra of different PMFs, birefringences (n) and PCs state were obtained through numerical simulation. The experiment was done and the results indicated that the wavelength spacing was determined by PMF length and birefringence (n), the transitivity by PC state and transmission peak by PMF and PC state. The experimental results agreed with the theoretical analysis.