Objective: to evaluate the clinical effica-cy and safety of ultra-early lumbar puncture drainage of cerebrospinal fluid (CSF) in patients with aneurysmal sub-arachnoid hemorrhage (SAH). Methods: patients (n = 140) with aneurysmal SAH were randomly divided into obser-vation group (n = 70) and control group (n = 70). After ad-mission, CSF was drained by ultra-early lumbar puncture in the observation group and intermittent lumbar puncture after aneurysm operation in the control group. The inci-dences of early aneurysm rupture, acute hydrocephalus and delayed hydrocephalus were compared between the two groups. Results: there was no significant difference in the incidence of early-ruptured aneurysm and acute hy-drocephalus between the two groups, but the incidence of delayed hydrocephalus in the observation group was sig-nificantly lower than that in the control group. Conclusion: ultra-early lumbar puncture drainage of CSF in aneurysmal SAH can effectively reduce the incidence of long-term de-layed hydrocephalus and it is a safe and effective treatment.