The conversion process of the polycarbosilane (PCS) into silicon carbide (SiC) was investigated by TG-DTA, infra-red spectrum analysis (IR) and X-ray diffraction (XRD) etc, which indicated the quasi ceramic characteristics of pyrolyzates treated at 600℃. The carbon fiber reinforced silicon carbide (C_f/SiC) composites were hereby prepared at 600℃ through precursor infiltration and pyrolysis (PIP), and polycarbosilane (PCS) acted as precursor, carbon fiber as enhanced fiber. The results show that bending strength of 3D-C_f/SiC composites are 193.69MPa, room tensile strength 197.69MPa, high temperature(600℃) tensile strength 167.33MPa. Noticeably, the density of 3D-C_f/SiC composites is just only 1.27g/cm³. Furthermore, the fracture surface and microstructure were analyzed and discussed too.