Objective To investigate the effect of severe eraniocerebral injury patients with hypernatremia.Methods Review and analysis of 356 cases of severe craniocerebral injury and 185 cases of hypernatremia. Analysis on the relationship between hypernatremia and prognosis. Results The 185 eases of severe craniocerebral injury with hypernatremia, the incidence is 52 %. Including 136 death cases, the mortality rate was 73.5 %. Hypernatremia appeared after admission since 1～18 days,the average days for this were 4.1 days. 69 cases appeare hypernatremia in 24 hours,60 cases in 48 hours,16 cases in 72 hours,145 cases of hypematremia appeared after admission within 3 days,about 78%. Blood sodium level was 148～196mmol/L, average was 172mmol/L, duration time was 1～25 days, average was 5.4 days. Conclusion It seems that almost hypernatremia appeared, when severe crartiocerebral was injuried in 3 days. The mortality is very high.