SiBCN based metastable ceramics and their composites possess unique microstructure and excellent high-temperature performance, and exhibit significant application potential under harsh conditions such as high-temperature oxidation, severe thermal shock, and gas flow ablation. This review focused on the SiBCN based metastable ceramics and their composites by mechanical alloying, summarized the research progress on the microstructure characteristics and evolution, mechanical properties, oxidation resistance, thermal shock resistance, and ablation resistance of SiBCN based amorphous ceramic powders and bulk ceramics based on mechanical alloying technology in recent years, also in comparison with the polymer derived counterparts. The future research focus and development trend of SiBCN based metastable ceramics with higher performance were finally pointed out.