An efficient light-trapping structure, which consists of the periodic Ag nanoparticles and a distributed Bragg reflector (DBR) with high reflectivity, is presented for the thin-film gallium arsenide (GaAs) solar cells. The effects of both Ag nanoparticles and DBR on the optical absorption of GaAs solar cells are theoretically investigated by using finite- difference time-domain (FDTD) method. The optimization process of parameters for the solar cell with both structures is analyzed systematically. The great absorption enhancement in GaAs layer is demonstrated, especially in the wavelength region near the GaAs band gap. It is observed that the superposition of the two effects excited by Ag nanoparticles and DBR results in the obvious absorption enhancement. By using cylindrical Ag nanoparticles and DBR together, the maximum enhancement factor of the solar cell is obtained as 4.83 in the simulation.