To achieve perfect narrowband absorber, we proposed a simple three-layer thin film (MDM) structure and developed a theoretical model. A comprehensive investigation was conducted on this structure through a combination of simulations and theoretical calculations. First, we executed theoretical calculations on the structure using both finite-difference time-domain algorithm (FDTD) and transfer matrix algorithm. The effects of several structural parameters on the absorption spectrum were analyzed in this study. We analyzed and discussed the physical mechanism of narrow band perfect absorber structure caused by the structure. Finally, we successfully used magnetron sputtering as a fabrication method to produce three-layer samples. The experimental results were consistent with the theoretical simulation. Our proposed structure for a narrowband perfect absorber can achieve a maximum narrow bandwidth of approximately 21 nm and a maximum absorption of 99.51%. We establish a strong basis for related applications by achieving perfect narrowband absorption.