Due to the excellent photothermal properties, plasmonic nanofluids have been intensively studied in the field of solar thermal utilization. Metallic nanoparticles, such as Au and Ag, of different shapes have been widely investigated taking advantage of the localized surface plasmon resonance (LSPR) effect. However, the nanoparticles which can excite magnetic resonance apart from the LSPR effect have been rarely studied. In this study, a core/shell/shell shape Ag-SiO2-Ag composite nanoparticle has been proposed for exciting both magnetic resonance and LSPR, giving rise to multiple absorption peaks and broadband absorption. The resonance modes have also been investigated by analyzing the local electromagnetic field. In addition, the effects of size parameter and material of the nanoparticles on the optical properties have been studied to explore the possibility to broaden the absorption peaks. The findings in this work suggest that the core/shell/shell shape metal-insulator-metal composite nanoparticles can be promising candidates for solar thermal harvest.