Field enhancement due to the surface plasmon effect is particularly attractive for surface-based nonlinear optics as the efficiency of most nonlinear phenomena can be greatly enhanced. Potential applications include nanophotonics and spectroscopy where nonlinear optical processes play an important role. Isolated metal particles as well as patterned substrates have been studied to enhance various nonlinear phenomena such as Raman scattering, four-wave-mixing (FWM), etc. This article illustrates the use of Synopsys’ RSoft Photonic Device Tool, FullWAVE, with its FDTD algorithm for a plasmonic nanocavity grating. The structure, composed of nanogrooves in a gold film, combines local resonances of the nanocavities with grating resonances that involve surface plasmon polaritons (SPPs) generated on the corrugated surface to enhance FWM nonlinear phenomena.