The invention relates to a back surface detection type SERS (surface-enhanced Raman scattering) chip and a preparation method thereof, and belongs to the technical field of SERS. The SERS chip is a polymer-metal composite material. The preparation method of the SERS chip comprises the following steps: copying an AAO (Anode Alumina Oxide) template structure by using a polymer, so as to obtain a polymer coronary array with the surface structure complementary to the AAO surface structure; further constructing a noble metal layer with SERS activity on the surface of the polymer coronary array, so as to obtain the SERS chip. Through the adoption of the manufacturing technology and the selected chip material, the two sides of the chip are different in medium material and surface roughness; experiments and theoretic simulation prove that surface plasma can be more effectively excited and coupling can be realized on the premise that the back surface detection manner is adopted for the chip, so as to obtain stronger SERS signals.