NOVELTY - Biologically preparing gamma -aminobutyric acid, comprises preparing bacterial cells, filtering and collecting cells by a ceramic membrane, producing gamma -aminobutyric acid by preparing buffer liquid, adding bacterial cells, separately adding the substrate sodium glutamate, producing gamma -aminobutyric acid by secondary fermentation and then collecting supernatant by centrifugation; filtering supernatant, decoloring, adopting electroosmosis, stopping circulation and collecting supernatant of gamma -aminobutyric acid, and preparing gamma -aminobutyric acid powder product or gamma -aminobutyric acid crystal product.    USE - The method is useful for biologically preparing gamma -aminobutyric acid.    ADVANTAGE - The method: utilizes the free lactic acid bacterial cells for catalyzed synthesis of gamma -aminobutyric acid, helps to improve the production technology to improve the gamma -aminobutyric acid yield, reduce the production cost, and establishes a method for preparing high-purity gamma -aminobutyric acid; and utilizes the reaction system free of carbon sources, nitrogen sources and other culture components, and utilizes the reaction liquid with components that are simple relative to the fermentation liquid, which can greatly improve the purity of the product, and ensures simple post-treatment, short production cycle, less environmental pollution and low production cost.    DETAILED DESCRIPTION - Biologically preparing gamma -aminobutyric acid, comprises: (a) adding 1-30 g/l sodium glutamate into a culture medium as an inducer, performing induced enzyme production, inoculating strain for producing intracellular glutamic acid decarboxylase and culturing at 25-35 degrees C, adding a base in the fermentation process to control the pH value so that the pH value of fermentation liquid is maintained at 4.5-7, culturing for 8 to 24 hours, and obtaining bacterial liquid after the culturing process is finished; (b) filtering the bacterial liquid obtained in the step (a) using a ceramic membrane and collecting the cells, where the pore size of membrane is 0.05-1 mu m, and obtaining the cells; (c) preparing 0.01-0.5 mol/l buffer liquid of 3-7 pH value, adding 10-100 g/l bacterial cells, separately adding the substrate sodium glutamate (0-30 g/liter concentration), producing gamma -aminobutyric acid by secondary fermentation under 28-40 degrees C reaction temperature for 10-50 hours, and collecting the supernatant by centrifugation after the fermentation is finished; (d) filtering the supernatant obtained in the step (c) to further remove the bacterial cells, and obtaining the supernatant; (e) regulating the pH value of the supernatant obtained in the step (d) to 7-8, and decoloring by a granular activated carbon, and collecting the supernatant; (f) adopting electroosmosis to remove impurity, maintaining the pH value of the supernatant at 7-8, stopping circulation when the electrical conductivity is reduced to less than or equal to 1000 mu Siemens/cm, and collecting the supernatant of gamma -aminobutyric acid; and (g) preparing the gamma -aminobutyric acid supernatant obtained in the step (f) into gamma -aminobutyric acid powder product or gamma -aminobutyric acid crystal product.