Abstract: To address the complex procedures and reliance on chemical reductants in conventional noble metal nanomaterial synthesis, a continuous-flow synthesis strategy was proposed by coupling a microchannel reactor with dielectric barrier discharge （DBD） plasma. HAuCl₄ was reduced by plasma within the microchannel to generate AuNPs, and combined with Al₂O₃ to form Au@Al₂O₃ nanoparticles. The effects of HAuCl₄ concentration, residence time, and plasma power on the products and their surface-enhanced Raman scattering （SERS） performance were systematically investigated. The results showed that optimal synthesis conditions were: HAuCl₄ concentration of 0.5 mmol·L⁻¹, residence time of 6 seconds, and plasma power of 5.5 W. The SERS substrates constructed using Au@Al₂O₃ nanoparticles exhibited high sensitivity and stability in detecting various analytes. In particular, the detection limit for rhodamine B reached as low as 10⁻¹² mol·L⁻¹, with quantitative detection achievable over the range of 10⁻⁴ to 10⁻¹² mol·L⁻¹. These findings provide guidance for the efficient and controllable synthesis of functional nanomaterials.