The grating/nanoparticle hybrid structure is designed to improve the enhancement effect of surface-enhanced Raman scattering (SERS) substrates. The extinction characteristics and the optical field distribution of the structure are simulated through the finite-difference time-domain (FDTD) method. Meanwhile, the effect of the coupling between the propagating surface plasmons (PSPs) of gratings and localized surface plasmon resonance (LSPR) of nanoparticles are discussed. Given the LSPR wavelength of two Au nanoparticle arrays (with the interparticle spacing of 2 nm and 6 nm, respectively), when the wave vector components of PSP and LSPR of diffraction gratings along the x axis are identical in view of the matching principle of resonance wavelength of LSPR and PSP, two Au gratings with different periods are designed to match two Au nanoparticle arrays separately. When the gratings are excited by plane waves, they generate PSP to excite LSPR of nanoparticles. FDTD simulations demonstrate that the square of maximum electric field intensity in the particle gaps of the grating/nanoparticle hybrid substrate is improved by one order of magnitude compared to that of the corresponding nanoparticle array under 633 nm excitation. Meanwhile, unlike the situation where LSPR is directly excited by plane waves, the electric field intensity around the particles in the hybrid structure excited in which LSPR is excited by PSP is enhanced, and the hot spot area is largely extended, and thus more molecules are in the area of high enhancement, which is highly conducive to improving the overall SERS signal intensity of those molecules dropped on the substrate.