SR-249, a kind of polysiloxane (PSO), was used as the precursor for the first time to fabricate carbon fiber cloth reinforced silicon oxycarbide (2D Cf/Si-O-C) composites. The cure and pyrolysis of the SR-249 as well as the mechanical properties, oxidation and thermal shock behavior of the composites were investigated in the paper. The flexural strength and fracture toughness of the composites reached 217.6 MPa and 12.5 MPa·m1/2, respectively. After soaked at 1300°C under the static air for 10 min, the composites retained 58.5% flexural strength and 64.5% fracture toughness. The thermal shock behavior of the composites was studied by water quenched method. The composites retained 49.3% flexural strength and 47.4% fracture toughness after 10 times of quenching from 1200 to 20°C.