A 2D C/SiC-BCx composite was tested under static load in both wet oxygen and dynamic combustion atmospheres. The microstructural evolution and self-healing mechanisms of the composites were investigated by a scanning electron microscope. The results indicated that the multi-scale deflection of cracks played an important role in improving the performance of 2D C/SiC-BCx in both atmospheres. The glass phase could seal the matrix cracks and flow into the fiber bundles through the cracks. As a result, the fibers and fiber/matrix interface within 2D C/SiC-BCx were protected from oxidation. The retention rate of high-temperature tensile strength of 2D C/SiC-BCx got a significant improvement in wet oxygen atmosphere at 700 °C, compared with 2D C/SiC. The damage rate of 2D C/SiC-BCx remained in a smaller scope in dynamic combustion atmosphere. The damage rates of the 2D C/SiC-BCx were about 80% and 90% lower than that of 2D C/SiC, respectively at 700 and 900 °C.