The invention relates to a construction method and an application of high-yield gamma-aminobutyric acid recombinant escherichia coli / pET-28a-1pgad, in particular to a genetic engineering bacterium construction method, recombinant enzyme enzymology property study and an application to the conversion of L-glutamic acid for producing gamma amino butyric acid (GABA), which belongs to the technical field of biology in the fermentation engineering. Firstly, lactobacillus plantarum GB 01-21 glutamic acid decarboxylase (GAD) genes are obtained through polymerase chain reaction (PCR) amplification, recombinant plasmids pET-28a-1pgad are constructed, in addition, the successful expression is realized in E.coli BL21(ED3), secondly, Ni column affiliation chromatography purification is adopted on crude enzyme liquid for obtaining recombinant GAD, in addition, the enzymology property of the recombinant GAD is primarily studied for guiding the optimization of conversion conditions, finally, conversion experiments are carried out on a 5L fermentation tank, the GABA accumulation concentration can reach 204.5g / L, the mol conversion rate is 97.92 percent, and good foundation is made on the further industrial application.