SiC/SiBCN composites were prepared by SiC fiber as the reinforcing phase and SiBCN composite ceramic precursor as the impregnating agent. The composition, morphology and mechanical behavior of SiC/SiBCN composites before and after oxidation were analyzed by SEM and mechanical properties tests. The results show that with the increase of PBN content in SiBCN composite ceramic precursors, The quality retention of precursor ceramics increases first and then decreases, and the retention of SiC/SiBCN composites under 1000 ℃ after 20h oxidation increases first and then decreases. This is mainly due to the increase of the PBN content in the SiBCN multiphase ceramic precursor, which is beneficial to the increase of the crosslinking degree of the precursor molecules, and easier to form a stable three-dimensional network structure. In addition, porosity and oxidation behavior of SiBCN multiphase ceramics also affect the oxidation stability of SiC/SiBCN composites.