NOVELTY - Preparing D-cysteine, comprises e.g. adding pure water in a reaction kettle and adding processed DL-cysteine powder and then stirring to make DL-cysteine completely dissolved, adjusting the pH value of the material liquid to 2 using hydrochloric acid, maintaining the temperature of the material liquid at 35-40 degrees C using a constant temperature system, adding concentrated tryptophanase culture liquid in the reaction kettle and stirring and then reacting, and heating the material liquid using the constant temperature system after the reaction is finished.    USE - The method is useful for preparing D-cysteine, which is useful as chiral medicine intermediate in third generation cephalosporin antibiotic (cefminox sodium) (claimed).    ADVANTAGE - The method allows simple and convenient preparation of D-cysteine with high purity in an eco-friendly manner.    DETAILED DESCRIPTION - Preparing D-cysteine, comprises: (1) adding 2000 kg of pure water in a reaction kettle and adding 500 kg of processed DL-cysteine powder and then stirring to make DL-cysteine completely dissolved, adjusting the pH value of the material liquid to 2 using hydrochloric acid with the concentration of 30%, maintaining the temperature of the material liquid at 35-40 degrees C using a constant temperature system, adding 2 kg of concentrated tryptophanase culture liquid in the reaction kettle and stirring and then reacting for 11-13 hours, heating the material liquid to 70 degrees C using the constant temperature system after the reaction is finished, and adding 40 kg of active carbon and then stirring and decoloring for 5 hours; (2) adding the material liquid into a filter press by a pump and a pipeline and then performing solid-liquid separation to obtain purified clear liquid, refining the clear liquid into a neutralizing kettle by a pump and a pipeline, and adjusting the pH value of the solution to 5.89 using ammonia water with the concentration of 30% and then crystallizing and stirring for 5 hours; (3) introducing the crystal liquid into a centrifuge for solid-liquid separation, where the obtained solid is L-tryptophan, promoting target molecule crystallization by acid dissolving and alkali refining method and then drying, packing and storing, introducing the obtained clear liquid into a concentration kettle, concentrating the half of the original vn the concentration kettle and thenolume using steam negative pressure and directly adding active carbon i filtering when it is hot and stirring for 5 hours, and introducing the plate-frame filter supernatant liquid to the crystallizing kettle; and (4) adding cooling salC, starting the stirret water of the clear liquid in the crystallizing kettle for cycling to 0-3 degrees r and then stopping stirring, keeping constant temperature for 12 hours still crystal and then performing solid-liquid separation to obtain wet D-cysteine and drying using a dryer using negative pressure at 40-46 degrees C for 5-6 hours, and introducing the dried agglomerate to a crusher to crush and then packaging and storing.