〔Abstract〕 Objective To analyze the correlation between the optic nerve sheath diameter (ONSD) and intracranial pressure (ICP) in patients with severe traumatic brain injury. Methods The subjects of the study were 40 patients with severe head injury admitted to the First Affiliated Hospital of Gannan Medical College between January 2020 and February 2021. They were randomly divided into observation group and control group, with 20 cases in each group The observation group used critical ultrasound to dynamically monitor the changes of ONSD; the control group used critical ultrasound to dynamically monitor the changes of ONSD combined with intraventricular tube pressure measurement to record the changes of ONSD and the results of patients' ICP in the two groups. Results In the control group, those with elevated ICP at the same time point had significantly higher ONSD than those with normal ICP, and the difference was statistically significant (P < 0.05); patients’ ICP and ONSD were positively correlated (r = 0.748, P < 0.05); There was no statistically significant difference in ONSD between the two groups of patients at the same time point (P > 0.05); the difference in survival rates between the two groups of patients was not statistically significant (P > 0.05). Conclusion The ONSD of critically ill ultrasound can be used as an important basis for judging the ICP of patients with severe craniocerebral injury. The obvious increase of ONSD indicates that the ICP of patients is increasing, and timely intervention measures are needed.