Subungual herniation of the cerebellum is a congenital malformation of the posterior cranial fossa cerebellum that develops between the ages of 15 and 65, with a predominance of middle-aged adults. The first symptoms include unexplained pain in the occipital neck and upper arms, numbness in the fingers, or concurrent vertigo, tinnitus, diplopia, unsteadiness and weakness in walking, as well as separation of deep and superficial senses, limb motor dysfunction and muscle atrophy, etc. Very few patients show scoliosis without any of the above symptoms. I once operated on a 16-year-old girl who came to our spine surgery department to have scoliosis corrected by Prof. Yang Junlin. The diagnosis can be made on the basis of imaging combined with clinical manifestations (headache, compression of posterior brain structures, spinal cord symptoms, hydrocephalus, etc.) on MRI scan in sagittal position with one or both cerebellar subungual herniation exceeding the foramen magnum margin by less than 5 mm. Once the diagnosis of Chiari malformation combined with spinal cord cavitation is made, hospitalization and surgery should be promptly performed to control the serious consequences of further progression of the disease. We use posterior cranial fossa decompression (PFD) and occipital pool reconstruction with an outcome of over 90%. The root cause of Chiari malformation is the herniation of the lower part of the cerebellar tonsils into the foramen magnum due to congenital hypoplasia and small volume of the posterior cranial fossa. Therefore, the principle of surgical treatment is to relieve the compression of the hindbrain and spinal cord, and to re-establish the physiological circulation of the cerebrospinal fluid. During surgery, the volume of the posterior cranial fossa must be enlarged, the greater occipital pool must be reconstructed, the subarachnoid space must be restored, and the cerebrospinal fluid circulation must be restored.