The invention relates to a die forging forming method for 15-5PH stainless steel and relates to the technical field of 15-5PH die forging. By adding pre-forged die design in an original 15-5PH die forging technique, 15-5PH materials are sufficiently deformed in a pre-forged die, only the undervoltage amount of 5-6 mm is reserved for a finish-forging die, and 15-5PH finish-forging deforming resistance is reduced. Therefore, according to the die forging forming method for the 15-5PH stainless steel, abrasion of the finish-forging die is greatly reduced, reliability and stability of the size of a forge piece are ensured, the service life of the die is prolonged, and a novel selecting way is provided for a large 15-5PH die forging technique.