There are two types of hydrocephalus after traumatic brain injury: acute and chronic. Generally, there is not much difficulty in diagnosis based on medical history, cranial CT, MRI scan and lumbar puncture manometry + diagnostic release of cerebrospinal fluid (40 ml). However, we have found that many clinicians, even senior doctors, tend to use the low pressure of lumbar puncture as a basis for denying the existence of post-traumatic hydrocephalus, thus delaying the treatment of many patients. In fact, with a little statistical knowledge it is not difficult to understand that the clinical reference range is the range in which the majority of normal people are observed. It usually refers to 80%, 90%, 95%, 99%, etc. The most commonly used is 95%. Here there is a problem of false positive and false negative rates, that is, a person with normal lumbar puncture pressure may also have hydrocephalus. Conversely, there is a certain probability that those who do not have normal lumbar puncture pressure will not have hydrocephalus. The reference value of adult lateral lumbar puncture pressure is 70-180 mmH2O, which is a very large range. Therefore, for those whose pressure is within the reference value, if CT examination after trauma shows obvious enlargement of the ventricle and deepening of the sulcus, but the two are not proportional, and the enlargement of the ventricle is more obvious, especially the periventricular hypodensity; MRI scan shows dilatation of the anterior horn of the lateral ventricle and interstitial edema band around the ventricle, it should be highly The suspicion of normal post-traumatic cranial pressure hydrocephalus should be high. At this point, diagnostic lumbar puncture is essential. If the cerebrospinal fluid pressure is lower than 180 mmH2O in the lateral recumbent position, a definitive diagnosis can be obtained after lumbar puncture releasing 40 ml of cerebrospinal fluid and temporary improvement of the patient’s symptoms and signs. Ventriculo-abdominal shunt surgery is the current treatment of choice, and for pressures higher than 140 mmH2O, a medium pressure shunt can be used. However, for pressures below 140 mmH2O, a low-pressure or low-pressure shunt device is always recommended.