The invention provides a method for utilizing a lactobacillus fermented agricultural and sideline product to prepare gamma-aminobutyric acid, and belongs to the technical field of biological processing of agricultural and sideline products. The method comprises the steps that S1, lactobacillus bacterial suspension liquid is prepared; S2, lactobacillus is fixed; and S3, the fixed lactobacillus obtained in the step S2 is inoculated to a liquid culture medium containing the agricultural and sideline product and sufficiently stirred, and the liquid ferments. Lactobacillus is fixed by utilizing sericin, cellulose and oxidized dextran containing polyaldehyde, and the lactobacillus fermented agricultural and sideline product has the characteristics that the biocompatibility is high, the product is safe and non-toxic, the stability is good, and multiplication of lactobacillus is promoted. The waste agriculture and sideline product is adopted to be a fermentation culture substrate, resource recycling is achieved, and the obtained fermented liquid contains the nutrient matter in the agricultural and sideline product and a great amount of gamma-aminobutyric acid, and has the very high nutrient value.