The invention belongs to the technical field of chiral compounds biological transformation separation, in particular relates to a method for preparing chiral organic coumounds and a method for preparing D-
ornithine and
putrescine, and is also suitable for preparing other D-
ornithine compounds and
aliphatic amine. The method for preparation comprises: mixing L-
arginine or salt of the L-
arginine with salicylal or derivant of the salicylal according to proportion, dissolving in alkaline or acidic dissolvant, obtaining DL-
ornithine after
racemization reaction, taking the DL-ornithine, biotransforming with
microorganism or
enzyme which contains
lysine decarboxylase or
ornithine decarboxylase under the temperature from 25DEG C to 45DEG C, obtaining the D-ornithine and the
putrescine, then, using an
isoelectric point crystallization method or a cation exchange resin
separation method to separate the D-ornithine and the
putrescine, and obtaining optically pure D-ornithine and putrescine. A chemical
racemization method of the invention main takes water as the dissolvant, the catalyst consumption is little, the dissolvant which is used does not have poison and has low cost, the
microorganism is easily cultured, and the invention is suitable for large scale industrial production.