Abstract: In this paper, the combined blast and fragment loads due to close-in warhead explosion is simu-lated by placing prefabricated fragments at the bottom of bare TNT explosive, and the corresponding dam-age on I-core sandwich panels are evaluated using the software LS-DYNA. The differences of failure modes of sandwich panels subjected to only blast and combined blast and fragment loads are analyzed, and the effects of core configuration and thickness configuration between the front and back plates on the fail-ure modes are studied. The anti-damage performance of sandwich panels is then compared with that of the equivalent solid plate. In addition, the energy absorption characteristics of I-core sandwich panels under different loads are also analyzed. Numerical results show that the overall damage of both the sandwich pan-els and solid plates subjected to combined blast and fragment loads is more severe than that caused by blast only. The performance of I-core sandwich panels is superior to equivalent solid plates when the load-ing intensity is small. It is also found out that the loading intensity, loading type (blast loading or combined blast and fragment loading) and the thickness configuration between the front and back plates yield signifi-cant influences on the failure modes of the I-core sandwich panel. From the results of energy analysis, it can be concluded that the front face plate and the core are the main energy-absorbing parts under blast loading, while the front and back face plates become the main energy-absorbing parts when combined blast and fragment loading is considered.