Thermally-induced bias drift,i.e. Shupe effect is one of the challenges that improve the accuracy of interferometric fiber-optic gyroscope (IFOG). A thermally-bias-free scheme for an IFOG is presented,which is based on the different characteristic between the Sagnac effect and the Shupe effect that the Sagnac phase is related only to geometric layout of the sensing loop and is independent of the medium’s characteristic of light propagation. This paper exploits light propagations along two eigen-axes of the polarization maintaining fiber of IFOG to separate the rotation phase from the error phase. An experiment is designed based on two polarization mode propagates alternately in the sensing loop,and the feasibility of the theory is preliminarily verified. Meanwhile a detection scheme is also proposed that polarization mode changes alternately to improve the thermal performance of fiber optic gyroscope.