Abstract: The cross-linking and pyrolysis of hydrogen-containing polysiloxane(PSO) and divinylbenzene(DVB) were investigated in this paper. It was found that only catalyzed with H₂PtCl₆ could DVB/PSO cure completely. The mass ratio of DVB/PSO had a great effect on ceramic yield. The ceramic yield was the highest of 76 % when the mass ratio of DVB/PSO was 0.5. The content of Si, O, C in the product pyrolyzed at 1000 ℃ was 38.3 wt%, 27.4 wt%, and 34.3 wt%, respectively. Three-dimensional carbon fiber reinforced silicon oxycarbide composites (3D-B C_f/Si-O-C) were fabricated via precursor infiltration and pyrolysis using DVB/PSO as a precursor. The results indicated that the mechanical properties of 3D-B C_f/Si-O-C could be increased markedly if the first pyrolysis cycle was assisted by hot-pressing. The flexural strength and the fracture toughness of the composite, which was hot-pressed at 1600 ℃ for 5 min with a pressure of 10 MPa in the first pyrolysis cycle and treated subsequently with six cycles of vacuum infiltration and pyrolysis with a pressure of 1 atm, were 502 MPa and 23.7 MPa·m^1/2, respectively. The high properties were mainly attributed to the ideal interface microstructures.