The diagnostic criteria of central system leukemia include the presence of central nervous system symptoms and cerebrospinal fluid changes. 1. There are signs and symptoms of central nervous system, mostly manifested as headache, nausea, vomiting, visual impairment, convulsions, drowsiness, coma, hemiparesis, etc.. There may be cervical ankylosis, Kirschner’s sign, and optic papillary edema in the fundus of the eye. 2. cerebrospinal fluid changes, including the following changes: increased pressure, cerebrospinal fluid outflow of drops greater than 60 drops / min. white blood cell count greater than 0.01 × 10^9 / L. Smear see leukemia cells. Protein is greater than normal, and the Penn test gives a positive result. 3. Rule out other causes of similar changes in the CNS or cerebrospinal fluid. When the above symptoms occur, immediate examination in hospital is required to avoid delay.