The presence of herpes virus inside the cerebrospinal fluid is mostly due to herpes simplex virus infection. When a patient is infected with herpes simplex virus, the virus first causes primary infection in the oral and respiratory tracts and then retrogrades along the branches of the trigeminal nerve through the axons to the trigeminal ganglion, where it then lurks. When the body’s immunity is reduced, the virus is activated and invades the lobes of the brain directly from the respiratory tract or after oral infection the virus invades the brain via the trigeminal nerve, which leads to the presence of herpes virus inside the cerebrospinal fluid. Herpes virus inside the cerebrospinal fluid, it is recommended to go to the hospital in time for treatment, if not treated in time, the symptoms are serious, may be extensive brain substantial necrosis and cerebral edema, and may even cause death.