Objective To analyze the influence of drainage volume on prognosis of acute hydrocephalus(AHC)after aneurysmal subarachnoid hemorrhage(aSAH)by continuous lumbar drainage.Methods A retrospective trial was conducted on 82 AHC patients after aSAH admitted to the First Affiliated Hospital of Chongqing Medical University between January 2017 and January 2022.In 6 months after discharge,modified Rankin Scale(mRS)score was used to evaluate the prognostic outcomes.Univariate and multivariate logistic regression analyses were performed on demographic factors,severity of subarachnoid hemorrhage(SAH)at admission,medical history,cerebral vasospasm,and lumbar drainage data.Then a nomogram prediction model was constructed.Results Univariate analysis found that World Federation of Neurosurgical Societies(WFNS)score,Hunt-Hess grade,modified Fisher grade,time for continuous lumbar drainage,shunt dependence,cerebral vasospasm,and drainage volume were factors affecting the prognosis of the patients.Then logistic regression analysis revealed that high WFNS score(OR:3.25,95％CI:1.11～9.48),high modified Fisher grade(OR:3.66,95％CI:1.08～12.35),shunt dependence(OR:15.56,95％CI:1.22～198.57),and cerebral vasospasm(OR:22.24,95％CI:3.08～160.68)were independent predictors for mRS score,while volume of continuous lumbar drainage(OR:0.57,95％CI:0.40～0.82)was an independent protective factor.ROC curve analysis indicated a good predictive performance of the model(AUC=0.898,95％CI:0.935～0.861).Internal validation through Bootstrap method demonstrated excellent discriminatory ability of the model(C-index=0.950,95％CI:0.904～0.996;adjusted C-index:0.934).Conclusion Increased volume of lumbar drainage is an independent protective factor for poor prognosis following aSAH and can improve the prognosis of SAH patients.