The coupled nano-structure Ag@SiO₂ has both plasmon excitation like metallic nanoparticles and diffraction scattering like a dielectric nanosphere, which effectively controls the propagation path and the energy distribution of incident light and shows great potential applications in light trapping for thin film solar cells. In this work, we construct a three-dimensional electromagnetic model based on the finite-difference time-domain (FDTD) and rigorous coupled-wave analysis (RCWA) method to investigate the regulation mechanism of Ag@SiO₂ coupling structure to the spectral response of amorphous silicon cells. By being optimally designed, a high-efficiency cell device is achieved. The results show that the transmitted light into the active layer reaches a maximum value when Ag and SiO₂ have their feature sizes of 18 and 150 nm, respectively. The absorption spectrum of the corresponding cell device also arrives at its maximum value. The photoelectric conversion efficiency is enhanced from 7.19% to 7.80%, with an increment of 8.48% compared with the flat solar cell with an equivalent thickness of absorbing layer.