The invention discloses a method for coupling production of Gamma-polyglutamic acid by technologies of microbial fermentation and membrane separation. Aiming at solving the difficulties that the viscosity of fermentation liquor is continuously increased due to the product, namely polyglutamic acid, so as to have serious influence on the cell growth and dissolved oxygen supply in the fermentation process, the invention proposes a method for coupling the fermentation and separation. The method comprises the following steps of: strain activation, seed culture, fermentation culture, micro-membrane filtration, ultrafiltration concentration and feed supplementing. The method can lead the viscosity of the fermentation liquor to be maintained to lower level, thus being beneficial to increasing dissolved oxygen in a fermentation tank, reducing the inhibiting effect of high viscosity of the product to the cell growth, improving the yield of Gamma-PGA and fermentation yield, reducing the production cost and being beneficial to post treatment of the fermentation liquor and refining of the product. The method has mild operation condition, good stability, fastness, high efficiency, simple equipment and low investment, has common instructive significance to the production of high-viscosity biological polymer by microorganism fermentation and has wide application prospect in the industrial community.