The invention discloses a surface enhanced Raman scattering substrate and a preparation method thereof. The method comprises the following steps: firstly, growing a layer of gold nano film on a flexible polymer substrate, and enabling the gold film to generate regular and uniform cracks along with the extension of a polymer through adoption of a two-way mechanical stretching method; and then, transferring the gold film with the stretched microstructure to a clean glass substrate, and a layer of uniform and compact SnSe2 nanosheets grow on the gold film. The structure combines the advantages of a traditional metal SERS substrate, that is, a metal tip has a hot spot, and a local electric field is enhanced; and the two-dimensional material SnSe2 has the advantages that the two-dimensional material SnSe2 and the semiconductor SERS substrate are combined, surface non-uniformity caused by agglomeration due to weak adsorption capacity of the metal SERS substrate can be avoided, in addition, the two-dimensional material SnSe2 is large in specific surface area, the structure has a light limiting effect, and light can be limited in the structure. The advantages of a semiconductor SERS substrate and a traditional metal substrate are combined, and the effect of enhancing Raman scattering is achieved.