We demonstrate an Al/Si multilayer-grating microstructure covered on Si substrate. This microstructure presents a designable narrowband absorption in short-wave infrared (SWIR) waveband (2.0 μm-2.3 μm). We investigate its absorption mechanism by both modeling and simulations, and explain the results well with metal-insulator-metal and Fabry-Perot cavity theory. Furthermore, we present the absorption of fabricated multilayer-grating microstructure through experiment, and discuss the influence of structure's lateral angle on its absorption in detail. This work provides the possibility to design Si-based devices with designable working bands in SWIR spectrum.