Periodic paralysis is divided into three types: hypokalemic, hyperkalemic, and normokalemic, depending on the serum potassium concentration at the time of the attack. The main type of periodic paralysis associated with hyperthyroidism is hypokalemia. The normal range of serum potassium is 3.5 to 5.5 mmol/L. Lower than 3.5 mmol/L is considered hypokalemia. Hyperthyroidism with hypokalemic periodic paralysis can develop at any age, mostly in young adults (20-40 years old), more men than women; it mostly develops at night or in the morning after waking up; the main manifestation is symmetrical limb weakness, muscle weakness, often starting from the lower limbs and extending to both upper limbs, with the part near the trunk being heavier. Patients are clearly conscious, can speak normally, head and facial muscles are rarely affected, and eye movements are normal. However, severe patients may have respiratory muscle weakness, causing respiratory distress and even death. The interval between two attacks is normal; it can be 1 attack in weeks or months, and individual patients even have an attack every day; there are also those who have 1 attack in several years or only 1 attack in their lifetime. Common diseases that cause hypokalemic periodic paralysis include hyperthyroidism, primary aldosteronism, Guillain-Barre syndrome, mixed renal tubular acidosis, Cushing’s syndrome, and thymoma, among which hyperthyroidism is the most common.