  Observations show that there is a proton spectral "break" with E$_{break}$ at
1-10MeV in some large CME-driven shocks. Theoretical model usually attribute
this phenomenon to a diffusive shock acceleration. However, the underlying
physics of the shock acceleration still remains uncertain. Although previous
numerical models can hardly predict this "break" due to either high
computational expense or shortcomings of current models, the present paper
focuses on simulating this energy spectrum in converged two shocks by Monte
Carlo numerical method. Considering the Dec 13 2006 CME-driven shock
interaction with an Earth bow shock, we examine whether the energy spectral
"break" could occur on an interaction between two shocks. As result, we indeed
obtain the maximum proton energy up to 10MeV, which is the premise to
investigate the existence of the energy spectral "break". Unexpectedly, we
further find a proton spectral "break" appears distinctly at the energy
$\sim$5MeV.
