The invention discloses a medium, a strain and a method for fermentative production of polyglutamic acid through pea protein wastewater. The method includes the steps of (1), activation of the strain which refers to Bacillus subtilis LD-9308 collected in the general microbiological center of the China General Microbiological Culture Collection Center (CGMCC) with the number CGMCC NO. 13465; (2), preparation of seeds in shake flasks; (3), preparation of strain in seed-fermentation cylinders; (4), fermentation culture, to be specific, sterilizing a fermentation culture medium at the temperature of 115 DEG C for 30 minutes, cooling to the temperature below 38 DEG C, and inoculating the seeds in the shake flasks by the inoculum size of 1-3%. The medium for culture in the seed-fermentation tank comprises, 0.5-2.5% of glucose, 0.5-1.0% of ammonium sulfate, and the balance being pea protein wastewater. The fermentation culture medium comprises, 1-3% of glucose, 3-5% of glutamic acid or sodium glutamate, 2-4% of ammonium sulfate, 0.1-0.3% of dipotassium phosphate, and the balance being pea protein wastewater. The culture parameter in the step (4) includes: the temperature is equal to 37+/- DEG C, the rotating speed of stirring is equal to 150-250 rpm, the ventilation capacity in the front 10 hours is equal to 1 : (0.2-1) : 0.3 while the ventilation capacity in the later period is equal to 1 : (0.3-1) : 0.5, the culture time ranges from 20 to 25 hours, and the yield of polyglutamic acid ranges from 2.5% to 4.5%. The medium, the strain and the method have the advantages of low cost for medium raw materials, high yield, low total production cost and high environment friendliness.