Noble metal and semiconductor composite substrates possess high sensitivity, excellent stability, good biocompatibility, and selective enhancement, making them an important research direction in the field of surface-enhanced Raman scattering (SERS). Ta2O5, as a semiconductor material with high thermal stability, corrosion resistance, outstanding optical properties, and catalytic performance, has great potential in SERS research. This study aims to design and fabricate a composite SERS substrate based on Ta2O5 nanostructures, achieving optimal detection performance by combining the urchin-like structure of Ta2O5 with silver nanoparticles (Ag NPs). The urchin-like Ta2O5 nanostructures were prepared using a hydrothermal reaction method. The bandgap was modulated through structure design and the self-doping technique, the charge transfer efficiency and surface plasmon resonance effects were improved, thereby achieving better SERS performance. The composite substrate enables highly sensitive quantitative detection. This composite SERS substrate combines the electromagnetic enhancement mechanism (EM) and chemical enhancement mechanism (CM), achieving ultra-low detection limits of 10-13 M for R6G. Within the concentration range above 10-12 M, there is a good linear relationship between concentration and peak intensity, demonstrating excellent quantitative analysis capabilities. Furthermore, this composite SERS substrate is capable of precise detection of analytes such as crystal violet (CV) and methylene blue (MB), holding broad application prospects in areas such as food safety and environmental monitoring.