In a complex electromagnetic environment, magnetic field interference is one of the main reasons for the error of fiber optic gyroscopes. To reduce the influence of the magnetic field generated by the heating plate in the body of the fiber optic gyroscope on the accuracy of the gyroscope, a double-layer heating plate structure is designed, and a comparative analysis of the magnetic field at the fiber optic ring position above the single-layer and double-layer heating plates is carried out by using the finite element method, and the influence of the magnetic field on the accuracy of the fiber optic gyroscope is calculated based on the analysis results. The results show that the magnetic field of both heating plates is non-uniform at the location of the fiber optic ring. The magnetic flux density near the fiber optic ring to the heating plate has a ring-like distribution, while the magnetic flux density away from the heating plate has a strong center and weak center distribution. With the increase in the distance between the fiber ring plane and the heating plate, the maximum magnetic flux density of the single-layer heating plate on the fiber ring plane is about 30 to 122 times that of the double-layer heating plate. The magnetic sensitivity phase error of the fiber optic gyroscope varies sinusoidally with the direction of the magnetic field and the angle between the fiber ring. The phase errors of the magnetic field on the lower surface of the fiber ring are 1.299×10^-10 rad and 5.572×10^-12 rad, respectively. The above results prove that the magnetic field of the double-layer heating plate interferes with the fiber-optic gyroscope much less than that of the single-layer heating plate and that the electromagnetic interference generated by the double-layer heating plate is much smaller, which is more conducive to improving the accuracy of the fiber-optic gyroscope.