We propose a periodic structure as an extra absorption layer (i.e.,absorber) based on surface plasmon resonance effects,enhancing dual-band absorption in both middle wavelength infrared (MWIR) and long wavelength infrared (LWIR)regions.Periodic gold disks are selectively patteed onto the top layer of suspended SiNNO2/SiN sandwich-structure.We employ the finite element method to model this structure in COMSOL Multiphysics including a proposed method of modulating the absorption peak.Simulation results show that the absorber has two absorption peaks at wavelengths λ =4.8 μm and λ =9 μm with the absorption magnitudes more than 0.98 and 0.94 in MWIR and LWIR regions,respectively.In addition,the absorber achieves broad spectrum absorption in LWIR region,in the meanwhile,tunable dual-band absorption peaks can be achieved by variable heights of cavity as well as diameters and periodicity of disk.Thus,this designed absorber can be a good candidate for enhancing the performance of dual band uncooled infrared detector,furthermore,the manufacturing process of cavity can be easily simplified so that the reliability of such devices can be improved.