Development of high-performance microwave absorption materials (MAM) with stabilized magnetic properties at high temperatures is specifically essential but remains challenging. Moreover, the Snoke's limitation restrains the microwave absorption (MA) property of magnetic materials. Modulating alloy components is considered an effective way to solve the aforementioned problems. Herein, a hollow medium-entropy FeCoNiAl alloy with a stable magnetic property is prepared via simple spray-drying and two-step annealing for efficient MA. FeCoNiAl exhibited an ultrabroad effective absorption band (EAB) of 5.84 GHz (12.16–18 GHz) at a thickness of just 1.6 mm, revealing an excellent absorption capability. Furthermore, the MA mechanism of FeCoNiAl is comprehensively investigated via off-axis holography. Finally, the electromagnetic properties, antioxidant properties, and residual magnetism at high temperatures of FeCoNiAl alloys are summarized in detail, providing new insights into the preparation of MAM operating at elevated temperatures.