Abstract: 3D C_f/SiC anti-high temperature oxidation composites were prepared with low-molecular polycarbosilane (PCS) via precursor infiltration and pyrolysis (PIP) process, chemical vapor deposition (CVD) and powder sintering technology.FTIR, ¹H-NMR, gel permeation chromatography (GPC), TGA-DTA, XRD and TEM were used to research the structure and inorganic process of low-molecular weight PCS.Results show that the main structure of PCS may be [(-Si(CH₃, H)-CH₂-]n, the number average molecular weight of PCS is 420, its ceramic yield is approximately 70%, and PCS translates into β-SiC micro-crystal at 1 200 ℃.3D C_f/SiC composites and their members show good performance of anti-high temperature oxidation.