Objective To investigate the association between serum potassium level on admission and short-term prognosis in patients with aneurysmal subarachnoid hemorrhage.Methods The clinical data of patients with aneurysmal subarachnoid hemorrhage who were diagnosed and treated in the Department of Neurosurgery of Zhangjiajie People's Hospital between January 2014 and June 2018 were retrospectively collected. An ordered linear regression analysis was performed on the serum potassium level on admission, general status, Hunt-Hess grade, leukocyte count, PCO₂, and length of hospital stay of the patients meeting the inclusion criteria to explore the effect of serum potassium level on the short-term prognosis of patients and its possible mechanism.Results The ordered multivariate analysis showed that hypokalemia (0-3.5 mmol/L) was associated with poor short-term prognosis (P<0.05), with P<0.05 for the trend at a serum potassium level of 0-2.9 mmol/L, 2.9-3.1 mmol/L, and 3.5-5.5 mmol/L (all P<0.001). Other risk factors included Hunt-Hess grades I, Ⅱ, and Ⅲ, aneurysms located in the anterior communicating artery and the posterior communicating artery, and normal leukocyte count (P<0.05). The boxplot revealed that the serum potassium level showed a downward trend with increasing mRS14 score and the distribution interval of mRS14 score in the hypokalemia group was higher.Conclusions The lower the serum potassium level, the greater the likelihood of poor short-term prognosis, which leads to a longer length of hospital stay. Other possible factors are Hunt-Hess grade, aneurysm location, and leukocyte count.