A new diafiltration method for recovery of glutamic acid (GA) from ultrafiltration concentrate by continuously feeding isoelectric supernatants was developed. A developed model of GA recovery ratio was used to simulate the process of diafiltration with isoelectric supernatants, which demonstrated higher recovery ratio and water saving than the traditional dilfiltration with water. Coupled with the technique of distillation and isoelectric crystallization, the GA purity and yield were increased by 9.3% and 3.35% respectively. Then, a novel flow sheet of GA isolation from fermentation broth was formed.