Objective  To study causes of deterioration of sudden mydriasis in craniocerebral trauma patients with normal intracranial pressure and verify the efficiency of specific treatments. Methods  A retrospective analysis was performed on causes of four cases of accidental mydriasis in normal intracranial pressure among 473 cases of craniocerebral trauma treated from June  2008 to March 2012. Changes of patients’ condition and monitoring indices were observed after specific treatments. Results Abnormal mydriasis with synchronously normal intracranial pressure was largely due to sufficient decompression after a certain period of intracranial hypertension and persistence of brain perfusion pressure to more than  110 mm Hg or due to high cerebral perfusion pressure caused by redundant drainage of cerebrospinal fluid or low intracranial pressure（＜10 mm Hg）, together with factors like low plasma osmotic pressure and carbon dioxide accumulation. The study showed that the intracranial pressure was maintained normal, that the brain swelling took a turn for better, that medical condition were stabilized and that pupil returned to normal in the four cases after treatment with specific protocol. GOS was four points in three cases and five points in one during followup at six months postoperatively. Conclusion  Incidence of mydriasis with normal intracranial pressure in craniocerebral trauma patients can be efficiently declined through reduction of peripheral blood pressure, perfusion pressure controlling, hypertonic remedy maintenance and brain edema relief.