Abstract: A composite material of resorcinol-formaldehyde (RF) enhanced silica dioxide aerogel (RF/SiO₂) had been successfully synthesized by introducing RF to build a porous framework through the sol-gel technique, followed by ambient pressure drying to explore the possibility of the application of silica dioxide aerogel in electromagnetic microwave absorption. The RF/SiO₂ aerogel was then subjected to heat treatment, and its microstructure and physicochemical properties after heat treatment were characterized using SEM, XRD, and other methods. The influence of heat treatment temperature on the microwave absorption performance of RF/SiO₂ aerogel was investigated. The results show that the microwave absorption performance of RF/SiO₂ aerogel is significantly improved with increasing heat treatment temperature. At a heat treatment temperature of 1500℃, the RF/SiO₂ aerogel exhibits a minimum reflection loss of −48.42 dB at a thickness of 4.05 mm. At a thickness of 3.45 mm, the effective absorption bandwidth reaches 2.06 GHz, demonstrating excellent electromagnetic wave absorption performance. This study provides guidance for the preparation of high-performance microwave-absorbing materials.