Abstract: Abstracts: Currently, electromagnetic wave (EMW) pollution not only interferes with communication devices but also poses risks to human health. Furthermore, national defense and information security demand higher performance from EMW absorption materials. However, it is still challenging to fabricate electromagnetic wave-absorbing materials that simultaneously exhibit the characteristics of being "thin, light, wide, strong". In this study, boric acid (H₃BO₃) was added to polyvinylpyrrolidone (PVP)-polycarbosilane (PCS) precursor solution in a simple method to prepare boron-containing SiC fibers utilizing electrospinning and high-temperature pyrolysis. The physicochemical changes during the preparation process were analyzed using FTIR and TG-FTIR. The microstructure and composition of the fibers were characterized by SEM, TEM, XRD, Raman, XPS, and ICP-MS. The results revealed that the crystallinity of SiC in the fiber is poor, and most of them are microcrystalline surrounded by the amorphous phase of SiCxOy. The introduced small amount of H₃BO₃ exists in the amorphous phase in the form of B-O bonds. When the precursor solution composition was wt%(H₃BO₃)∶wt%(PVP)∶wt%(PCS) = 3∶10∶20, the boron-containing SiC fiber achieved a minimum reflection loss (RL_min) of -60.31 dB at a thickness of 3 mm, with an effective absorption bandwidth (EAB) of 7.44 GHz (10.56-18 GHz), completely covering the Ku-band (12-18 GHz). The existence of a variety of heterogeneous interfaces, polar covalent bonds, and three-dimensional conductive networks in boron-containing SiC fibers cause EMW to be reflected and absorbed within the material many times, thereby effectively absorbing electromagnetic waves and enhancing both the absorption strength and bandwidth. The boron-containing SiC fibers prepared by this method hold great potential for application in the field of EMW absorption.