Before and after oxidizing，the microstructures and properties of two typical continuous SiC fibers sintered at different temperature were systematically studied by SEM，TEM and XRD. It is found that the grain size gradually decreases from the surface to the core of the F-1 fiber sintered at high temperature，but the content of graphite phase increases slightly. The F-2 fiber sintered at low temperature is mainly composed of amorphous SiCO phase，which contains a great deal of nanometer SiC grains and graphite. The strength of the F-1 fibers is 1.74 GPa due to the holes，while the strength of dense F-2 fiber reaches 2.76 GPa. Both fibers are oxidized during heating in air at 1 000 ℃，and the oxide layers become thicker and the strength decreases with the prolongation of time. Although the grain boundaries act as diffusion channels of the F-1 fiber，the strength retention rate can still reach 55 % after 10 h oxidation. The high temperature oxidation resistance of the F-1 fiber sintered at low temperature is very low. After oxidizing for 10 h，the thickness of the F-2 fibers reaches up to 430 nm so that the strength is almost completely lost.