A fiber optic gyroscope design based on a new phase modulator mid-mounted structure is proposed. The scheme not only can overcome the shortcoming that the modulation frequency of the traditional fiber optic gyroscope is limited to the eigen frequency, but also can suppress the backscatter noise and polarization coupling noise. Theoretical analysis and experimental results show that the proposed structure can control the phase of the backscattered wave to the order of 10 ^-5, and the polarization coupling noise can be suppressed to 5×10 ^-8 (°)/Hz ^1/2. In addition, this mid-mounted structure can improve the bias stability of the gyroscope, which is increased from 0.11878 (°)/h to 0.09110 (°)/h. This scheme overcomes the technical problem of the fiber optic gyroscope influenced by eigen frequency, and provides a new way to suppress noise and improve accuracy.