Serum potassium 3.1mmol/L suggests mild potassium deficiency, which can be replenished by oral medication, and more serious, which requires prompt medical attention to find out the cause. Normal human serum potassium concentration is 3.5~5.5mmol/L, below 3.5mmol/L is called hypokalemia, severe hypokalemia may have serious consequences such as muscle pain, fatigue, or even respiratory muscle paralysis and cardiac arrest. Serum potassium of 3.1mmol/L belongs to mild potassium deficiency, which requires timely replenishment of potassium ions and searching for the cause of low potassium to prevent further life-threatening reduction of serum potassium concentration. Common causes of hyperkalemia include: excessive loss of potassium ions, such as diarrhea and vomiting; low intake of potassium ions, such as patients with difficulty in eating, prolonged bed rest, and tumors; it is also seen in Bartter’s syndrome and Gitelman’s syndrome. When supplementing potassium, remember to give priority to oral intake, urine volume is greater than 500ml/24h or 30~40ml/h before potassium supplementation, the concentration of potassium supplementation should not be more than 0.3%, and the rate should not be more than 20mmol/h. Serum potassium concentration should be detected in real time when supplementing potassium. Serum potassium 3.1mmol/L belongs to mild hypokalemia, it is recommended to consult a doctor in time to find the cause of hypokalemia and supplement potassium in time, blindly supplementing potassium has great risks.