In addition to a few congenital causes, cranial defects are commonly seen after traumatic skull fracture debridement, after decompression of bone flaps due to increased intracranial pressure, after removal of osteomyelitis lesions, and after resection of various tumors involving the skull. Cranial defects often cause physical and psychological stress to patients and keep them away from social life. Cranial repair not only protects the brain tissue in the cranial defect from direct trauma, but also restores the normal appearance of the skull aesthetically, thus enabling the patient to return to social life. It was found that after cranial repair, in addition to a significant improvement in cerebral blood flow on the affected side, the cerebral blood flow on the contralateral side was also improved. This led to the recognition of the importance of cranioplasty in improving and restoring brain function. The cranial brain is in the growth and development stage during childhood, and the cranial defects left after surgery will gradually change with growth and development. Parents of patients and even some medical professionals often ask, “When can a skull defect be repaired in a six-year-old child? Cranial repair can be performed in children about three months after debridement and decompression. In addition to timing, of course, the repair material is also critical, and polyether ether ketone (PEEK) is recommended. This material is a near-perfect cranial replacement material because of its excellent properties. Its elasticity, insulation, hardness, stability and other properties are similar to the human skull, and can be fused with the human skull.