Abstract: The superfluorescent fiber source (SFS) is an ideal source for fiber optic sensors (FOSs), because of the high stability. Relative intensity noise (RIN) of a SFS is proven to be an most important factor limiting the performance of FOSs. As the RIN cannot be suppressed effectively using an analog circuit, in this paper, a digital RIN suppressing system executed with intensity modulator was presented. To demonstrate this method, a semi-physical simulation was propose in which the RIN was reduced by 20 dB at the center frequency. This method is more effective than the former analog one by simulation. This digital RIN suppressing system is of great value to improve the performances of FOSs.