Based on quantum theory and multimode model, concluding the pump depletion, the second order quantum correlation as the function of interaction distance in stimulated Raman scattering (SRS) is calculated and analyzed. The analysis predicts that, in the absence of dispersion, the correlation between Stokes waves and the pump increases to unity when the increase rate depends on the ratio of the pump and input Stokes. In the limit, the results argee with the Raman generation theories and the semiclassical theories.