An infrared absorption model for microbolometer detection units with an umbrella-shaped absorption layer structure are established. Based on the optical admittance matrix method and impedance matching theory, the infrared absorption characteristics of the model under different aperture sizes and shapes of the umbrella structure are simulated using three-dimensional electromagnetic simulation software CST. The results show that the optical performance of the dual-layer umbrella-shaped aperture microbolometer is closely related to the aperture size of the umbrella structure. The introduction of the aperture in the umbrella-shaped microbolometer reduces the heat capacity of the detection unit while maintaining high infrared absorption characteristics, thereby improving device response speed. The resulting detection unit has an average absorption rate of 85% in the 8~14μm infrared band, meeting the design requirements of large-scale small-pixel non-cooled infrared focal plane detectors.