The influence of the mean wavelength of a broad-spectral source on the scale factor is analyzed. The systematic models of the scale factors for the open-loop and closed-loop fiber optic gyroscopes are preliminarily established. The mechanism influences of the mean wavelength and the second feedback loop on the scale factor are discussed in detail. The corresponding experiments are conducted. The experimental results coincide well with the theoretical analysis results and the validity of the proposed systematic model is verified.