Abstract: Three-dimensionally braided carbon fiber reinforced SiC(3D-B C_f/SiC) composites were fabricated through 8 cycles of vacuum infiltration of polycarbosilane(PCS)/divinylbenzene(DVB) and subsequent pyrolysis under an inert atmosphere. The effects of pyrolysis processes on the microstructure and mechanical properties of C_f/SiC composites were investigated. The results show that increasing heating rates can increase the density and result in better interfacial bonding leading to better properties of C_f/SiC composites. At the same time, one cycle of 1600℃ heat treatment could also increase the density and mechanical properties of C_f/SiC composites. It was found that the flexural strength of the C_f/SiC composites after pyrolysis by 15℃/min and one cycle of 1600°C heat treatment reached 556.7 MPa.