A math model that can describe the effect of stimulated Raman scattering (SRS) on pilot-tone detection technique is proposed. Through numerical simulation, it is shown that the effect of SRS could produce ghost-tones. The power of ghost-tones was larger for the channels separated further from the real-tone. The power ratio between real-tone and ghost-tones increases linearly with the increase of transmission length when propagation distance longer than 300 km.