Lumbar puncture is a common basic skill in clinical practice and is often performed by junior residents. But this skill has important implications. That is, why is a lumbar puncture performed? The first function is to measure the level of intracranial pressure, through the determination of the level of intracranial pressure, you can judge the condition, you can guide the use of drugs, for example, the patient’s cranial pressure is high, use dehydration drugs, not high can not use dehydration drugs; the second issue is the examination of the nature of the cerebrospinal fluid, to make a judgment on the patient. For example, if a patient has a fever and a stiff neck, is there an infection or not? If the patient’s cerebrospinal fluid is mixed, with high white blood cells, high red blood cells, high protein quantification, and low sugar and chloride, this is obviously a sign of infection, and the results of the culture support the existence of infection and the need for infection treatment; furthermore, lumbar puncture is also a diagnostic measure, that is, preventive treatment. For example, if a patient has hydrocephalus, whether it is appropriate to do a shunt or not, and whether there is any effect after the shunt, a lumbar puncture can be done to release part of the cerebrospinal fluid. The main symptoms of hydrocephalus are unstable walking, urinary incontinence and cognitive decline, which are the triad of hydrocephalus. If the cerebrospinal fluid is released and the patient’s triad of cognitive function, urinary incontinence, and unsteady walking improves, the shunt is worth doing. This is the role of lumbar puncture in the diagnosis and treatment of patients; another is that lumbar puncture can play a therapeutic role, for example, if there is an infection, we can inject drugs into the lumbar spine, which may be more direct and faster than the effect of intravenous drugs. These are the main four aspects of the role.