The invention provides a vibrating casting and forging composite forming method for aluminum alloy forgings and belongs to an aluminum alloy forging machining method. The vibrating casting and forging composite forming method for the aluminum alloy forgings solves the problems that by means of an existing casting and forging composite forming technology, the forging penetration is poor and the microdefect compaction effect is poor due to one-time compaction in the forging process, so that the forging defects are eliminated, and the forging performance is improved. The vibrating casting and forging composite forming method comprises the steps of alloy smelting, extrusion casting and vibrating die forging. By the adoption of the vibrating casting and forging composite forming method, the advantage that the forming performance of an aluminum alloy in the molten state is good and the advantage that through vibrating die casting, grains can be refined effectively and the density of the forgings is increased are combined; microdefect compaction during the casting process is promoted through high-pressure extrusion casting, the impact heating and stress wave superposition effect is generated through high-frequency vibration and compaction, the forging penetration is improved, the compaction and forge welding of the defects during the forging process are promoted, and the mechanical property is improved; and the vibrating casting and forging composite forming method has the beneficial effects that the technological process is short, the material utilization rate is high, energy is saved and the equipment investment is small and is especially suitable for forming of the complex aluminum alloy forgings of automotive steering knuckle control arms and the like.