As a commonly used food additive, synthetic dyes are widely used in foods such as beverages, sweets and dairy products, and in the food processing process. Excessive use of synthetic dyes may induce cell mutations, children’s hyperactivity, genetic diseases and even cancer, which greatly threatens human health. As a fast, cheap, stable, ultra-sensitive and accurate detection method, SERS detection can reflect rich information about molecular fingerprint through the vibration of the analyte, and accurately determine the trace quantity of synthetic dyes in the actual environment. The metal/semiconductor heterostructure formed by the combination of plasmon metal and semiconductor is advantageous for the enhancement of photoinduced charge transfer (PICT) efficiency, and has obvious advantages in the study of surface-enhanced Raman scattering. In this work, the prepared hybrid substrate is annealed to further improve the surface-enhanced Raman scattering activity. Initially, high-density and monodisperse silver/silver oxide (Ag/Ag ₂O) nanoparticles are loaded onto two-dimensional hexagonal boron nitride (h-BN) nanosheets. On this basis, by annealing the system at high temperature, an efficient charge transfer channel is constructed, which greatly improves the PICT efficiency and chemical enhancement (CM). It is confirmed experimentally that the SERS signal intensity of h-BN/Ag/Ag ₂O material annealed at 320 ℃ with crystal violet (CV) as probe molecule is significantly increased 18 times compared with that of unannealed material, enhancement factor (EF) reaches 16.3145 ×10 ⁷. Finally, based on the excellent SERS property of h-BN/Ag/Ag ₂O annealed at 320 ℃, the SERS detection of food additive Patent Blue V (PBV) is conducted in this work. The results show that the lowest detection concentration can reach 10 ^–12M, and the trace detection of synthetic dye PBV is realized. It has excellent spatial uniformity and anti-interference capability, which is of great significance in implementing the actual scene detection of PBV. The h-BN/Ag/Ag ₂O annealed at 320 ℃, the composite which is constructed in this paper, has both physical enhancement and chemical enhancement, and possess significant advantages in ultra-low sensitive SERS detection of food additives.