Aim To investigate the effect of different serum potassium concentration on in-hospital death in patients with heart failure. Methods Data of patients hospitalized for heart failure was collected in Department of Cardiology, Shengjing Hospital of China Medical University from January 2013 to December 2018 and a retrospective cohort study database was established. SPSS22.0 software was used for statistical analysis, independent sample t test, χ² test and Logistic analysis were used to clasify the effects of different serum potassium levels on in-hospital death of patients with heart failure. Results The in-hospital death of 9 459 patients with acute decompensation of chronic heart failure was 3.1%. The in-hospital death was the lowest (2.3%) when serum potassium was between 4.0～4.49 mmol/L, 4.2% for serum potassium ＜3.5 mmol/L, 7.7% for serum potassium 5.0～5.49 mmol/L, and 15.1% for serum potassium ≥5.5 mmol/L. Univariate Logistic analysis showed that serum potassium＜3.5 mmol/L and ≥5.0 mmol/L were associated with increased in-hospital death, and the same conclusion was reached after adjusting estimate glomerular filtration rate (eGFR) to exclude the effect of renal function. And the lower(＜3.5 mmol/L) or higher(≥5.0 mmol/L) the serum potassium level was, the greater the risk of in-hospital death. Conclusion Serum potassium level was significantly correlated with in-hospital death in patients with heart failure. The lower or higher the serum potassium level was, the greater the risk of in-hospital death. Maintaining serum potassium level between 3.5～4.49 mmol/L might be better for patients with heart failure.