With threonine deaminase (L-TD) and leucine dehydrogenase (L-LeuDH) obtained by cloning and expression as biocatalyst, the natural amino acid was converted into unnatural amino acid using the "one-pot" process.Finally, the product was obtained by crystallization, with a total yield of 84%.The configuration of the product obtained was confirmed by LC-MS and 1HNMR, with ee>99.9%.This process used cheap raw materials and enzymes, and avoided the intercurrent extraction and separation, holding out a bright prospect for an efficient and low-cost 2-aminobutyric acid production process.