An automatic nut-inserted injection molding system and a method of the same are provided, and the system includes an automatic feeding machine for providing a nut, an air-evacuating device, a robot arm for delivering the nut, and an injection-molding module. The injection-molding module includes a first mold block, a second mold block, an air passage and an air needle. The second mold block is detachably closed with the first mold block for mutually defining a molding cavity. The air needle is partially embedded in the second mold block. The air passage is formed in the second mold block, and respectively connected to the air needle and the air evacuation device.