The invention discloses a method for extracting polyglutamic acid from fermentation liquor through the aqueous two-phase technology. The method comprises the steps that a mixed solution is firstly prepared, and an aqueous two-phase extraction system is built, so that the mass fraction of PEG1000 ranges from 10% to 30%, the mass fraction of (NH4)2SO4 ranges from 5% to 25%, the mass fraction of the fermentation liquor is 10%, the pH value of the fermentation liquor ranges from 3.75 to 8.46, and then environment temperature is controlled to range from 20 DEG C to 40 DEG C; after the mixed liquid is subjected to natural phase separation, an upper phase is taken, and PEG1000 penetrates through an ultrafiltration membrane with the molecular weight cutoff of 30 KDa; finally, after the cut-off polyglutamic acid concentrated solution is subjected to low-temperature refrigeration at the temperature of -40 DEG C, vacuum freeze drying is carried out for 24 h at the temperature of -50 DEG C, and a pure product is obtained. The problem that polyglutamic acid fermentation liquor is thick, and consequently pretreatment cost is too high is solved, the subsequent aqueous two-phase system reaction is moderate, and damage of a traditional precipitation method to polyglutamic acid molecular weight is avoided.