Localized surface plasmon resonance (LSPR) is caused by the irradiation of light on a metal surface. Here we present a surface plasmon catalytic reaction at the gas-liquid-solid three phase interface. Electrochemical deposition was used to prepare Ag nanostructure/Cu mesh surface-enhanced Raman scattering (SERS) substrates. Surface wettability was adjusted by changing the processing time of the surfactant. Then a three-phase interface platform was constructed with good SERS performance and active surface plasmon catalytic capacity by droplet detection. At the gas-liquid-solid three phase interface, different oxygen supplies for the catalytic reaction were offered on surfaces with different wettability values. Thus, in this study, surface plasmon catalytic reaction of p-nitroaniline (PNA) was successfully in situ monitored and the reaction mechanism was explored. Otherwise, density functional theory (DFT) was used to calculate the Raman spectra and energy levels of the reactants and reaction products. Moreover, this work provides a new platform for monitoring the surface plasmon reaction at the gas-liquid-solid three-phase interface and contributes to the development of the study in the surface plasmon catalytic reaction field.