The most dangerous time is within three days after hitting the head, because within three days, many patients may develop brain contusion, brain hemorrhage, subdural hematoma, diffuse axonal injury and a series of other manifestations, like these are likely to aggravate sharply within three days and have an impact on the patient’s life, so It is important to review the head CT within three days to observe the trend of the disease. 7-10 days is mainly the peak period of brain swelling, and only by passing this period relatively smoothly can we have a more effective and safe prognosis in the follow-up, otherwise many patients may form chronic hydrocephalus, or intracranial infection and some other adverse reactions in the follow-up.