Raman scattering for doped GaAs/AlGaAs superlattice was measured at T=77 K. Two scattering peaks, whose Raman shift is 223 cm-1 and 422 cm-1, respectively, in Raman spectrum were observed. It is belived that two scattering peaks are related to coupling modes between plasmon and longitudinal optical phonon for Si-doped GaAs/AlGaAs superlattice. Calculated positions of Raman Scattering peaks produced by the coupling modes are in good agreement with measurement results.