Polarization maintaining fiber (PMF) resonator is the core component of a resonator fiber optic gyroscope. Polarization fluctuation induced by polarization coupling in resonator is one of the main sources of gyroscope’s measure error, and 90° docking of fiber polarization axis is an effective way to overcome the polarization fluctuations in resonator. In this paper, resonance characteristics and polarization characteristics of 90° docking in double couplers polarization maintaining fiber resonator are analyzed theoretically to obtain theoretical response curve, then sawtooth scanning method is experimentally used to obtain response curve with 24 finesse, 0.9615 resonant depth and 179.65° phase interval of the two polarization eigenstates. In consequence, good polarization characteristics of 90° docking in double couplers polarization maintaining fiber resonator are proved.