Surface-enhanced Raman scattering (SERS) is a highly efficient molecular spectroscopy technique widely used to detect trace species in studies in many fields such as chemistry, life sciences, and pharmaceutical analysis. However, the non-uniformity of “hot spots,” instability of chemical effects, and uncertainty of the number of molecules increase the volatility of Raman signals, which presents difficulty in their use for quantitative analysis. This paper introduces the principle of an internal standard method, improvement of substrate performance, and the modes for adding three internal standards, including external addition mode, core-internal standard-shell modes, and self-calibrating substrate mode, from the following four aspects: “hot spot” effect, chemical effect, molecular adsorption, and internal standard addition mode.