More and more observations show that large ground-level enhancement (GLE) events are often associated with twin coronal mass ejections (CMEs). In the twin-shock scenario, the preceding CME-driven shock provides an enhanced-level turbulence at the upcoming CME-driven shock. In this work, we focus on the GLE event on 2012 May 17, which would be associated with the twinshock interactions. Using the particle simulation method to examine the effect of the preceding CMEs being surrounded by the forthcoming CMEs on the energy spectrum. We use the preceding CMEs-driven shock to produce an enhanced seed population injecting into the later CME-driven shock for particle re-acceleration. As results, we simulate the twin-shock interactions and obtain the compound proton spectrum. Therefore we suggest that the twin-shock interactions would produce an GLE event with an “ankle-like” proton spectral slope.