Surface-enhanced Raman Scattering (SERS) technology has the advantages of high sensitivity, high resolution, non-destructive detection and no pre-processing. It has become a powerful tool for qualitative and quantitative molecular detection. The trace detection technology, which amplifies the Raman signal of the target analyte, can even provide rich structural information on the molecular level. Although the SERS enhancement mechanism has always been disputed, currently acknowledged enhancement mechanisms include physical enhancement (electromagnetic field enhancement) and chemical enhancement (principally contribution of charge transfer). With the application of metal, non-metal and other materials in SERS in recent years, many scholars have inspired extensive interest in the factors affecting the Raman signal enhancement of SERS substrate. Hence, it is of great significance to research the mechanism of SERS enhancement. In this review, the SERS enhancement mechanism is primarily elaborated on three aspects of the SERS electromagnetic enhancement mechanism, chemical enhancement mechanism and synergic mechanism, to analyze which factors affect the substrate enhancement effect and provide some references for the analysis of the SERS enhancement mechanism. At the same time, the problems faced by different base structures in the process of enhancement mechanism analysis were proposed: (1)In the electromagnetic enhancement mechanism, the single noble metal base had a great influence on the SERS electromagnetic enhancement mechanism due to its uneven distribution of “hot spots” and uncontrollable factors, which led to poor SERS sensitivity and repeatability. (2) In the chemical enhancement mechanism, the single semiconductor material was widely used in the SERS substrate due to its advantages of affordable price, stable material performance and easy surface modification. However, the effect on the SERS chemical enhancement mechanism was not obvious due to its low enhancement ability. (3)The SERS substrate is not limited to single metal or non-metal materials but more the combination of metal and non-metal.