The Raman enhancement factors of single molecule and multiple molecules in slot-waveguide coupling structure are analyzed and calculated theoretically by photon Green’s function in waveguide modes combined with the quantum optical form of molecules. The average enhancement factor, the Purcell factor and the percentage of waveguide collection are used as the main performance parameters to compare the difference between the independent slot-waveguide and the composite slot-waveguide. The results show that the composite slot-waveguide achieves a considerably higher Raman enhancement factor (two to three orders of magnitude higher than that of the slot-waveguide), which is mainly because of the combined increase of the electric field, the Purcell factor, the light-matter interaction volume, and the Raman signal collection efficiency.