It is very important to build uniform large-area dense hotspots to improve the surface-enhanced Raman scattering (SERS) detection limit. In our research, we designed and prepared a new flexibile SERS substrate with ultradense hot spots that has the advantages of high sensitivity, good repeatability, easy fabrication, and low cost. Due to the special dense hot spot structure, the substrate reaches a SERS enhancement factor of 2.1 × 1011. Because of the excellent physical stability of polydimethylsiloxane, the substrate can be bent at will, and the SERS performance will not change with bending. This is very important to extract effective detection objects on complex surfaces. The substrate has good light transmittance and softness and can be directly attached to the detected agricultural products to realize real-time and rapid SERS monitoring. This structure exhibits extraordinary performance for thiram detection in the ultralow concentration range of 10-13 M.