Abstract: Against the background of the widespread application of various electronic devices and communication technologies, there is great concern regarding the problem of excessive radiation of electromagnetic waves with regard to electromagnetic interference, environmental pollution, and human health. Microwave-absorbing materials (MAMs) can transform electromagnetic energy into heat or dissipate electromagnetic waves via interference. Numerous theoretical and experimental studies have focused on the prevention of electromagnetic pollution and other related problems. Magnetite (Fe₃O₄) is considered one of the most promising MAMs because of its excellent properties, such as high saturation magnetization, high Curie temperature, and low cost. However, the single Fe₃O₄ has the disadvantages of weak dielectric loss and easy oxidation, thereby limiting its application in the field of microwave absorption. Fabrication of Fe₃O₄-based nanocomposites is an effective solution for these problems. In this study, a new type of Fe₃O₄@SnO₂ composite similar to myrica rubra (Chinese bayberry) was synthesized by the Stöber method and hydrothermal method using magnetic Fe₃O₄ microspheres as template. The phase structure, surface elements, micromorphology, magnetic properties, and microwave absorption properties of the samples were characterized by means of X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, and transmission electron microscopy and by observations based on a vibrating-sample magnetometer and vector network analyzer. The results show that the diameter of the myrica rubra-like Fe₃O₄@SnO₂ sphere is about 500 nm, without obvious agglomeration, and that it has good morphological uniformity. The SnO₂ layer is composed of nano-SnO₂ particles, which are loosely stacked. The layer possesses many porous structures and is about 40 nm thick. The myrica rubra-like Fe₃O₄@SnO₂ has strong dielectric loss capacity, is conducive to improving impedance matching performance, and exhibits good electromagnetic wave absorption capacity. When the thickness is 1.4–2.8 mm, R_L(min) exceeds −20 dB. The optimum thickness is 1.7 mm, R_L(min) is −29 dB, and the effective bandwidth is 4.9 GHz (13.1–18 GHz). It is a potential-absorbing material.