We perform full elastic wavefield simulations of Weihe basin during the great Wenchuan earthquake using a 3-D spectral element method. The 3-D basin model, including Quaternary and Tertiary layers, is constructed based on the drilling well data and seismic profile data. The source model of Wenchuan earthquake was inversed using the far-field P waves by non-negative linear least-squares inversion method. We validated the source, crustal and basin models by comparing synthetic and observed records of three-component displacements at 28 stations distributed within and at the edge of the basin. Results indicated that direct surface waves incident to the basin were trapped and rebounded obviously at the two deepest bowls where the Quaternary thicknesses are >1000 m, with shaking duration of large-amplitude ground motion about 50–100 s longer than that outside the basin. The southern steep basin boundary induced noteworthy large-amplitude surface wave, propagating and reflecting in the basin, which increased the wave amplitude and prolonged the shaking duration. The basin produced remarkable amplification in frequency range 0.125–0.175 Hz by a factor of about 6–10, attributed to the reverberation of the deepest part of sediment within the basin. The amplification of basin is coherent to the Quaternary thickness, with deep Quaternary sediment corresponded to the large-amplitude and long-duration ground motion.