Diabetic hyperosmolar coma, now known as diabetic hyperosmolar hyperglycemic syndrome, is a serious acute complication of diabetes mellitus. Patients are characterized by severe hyperglycemia, high plasma osmolality, and dehydration. Patients often have varying degrees of impaired consciousness and even coma, often without significant ketosis. This acute complication is commonly seen in older diabetic patients, usually with blood glucose over 33.3 mmol/L, often with elevated blood sodium concentrations, and negative or weakly positive urinary ketone bodies. Because the patient is severely dehydrated, treatment begins with massive fluid replacement, usually with saline followed by hypotonic fluids depending on blood sodium levels. If the patient is comatose, the gastric tube can be lowered and warm boiled water can be injected through the gastric tube, which is also a route of rehydration. Wait until the blood glucose drops below 13.8mmol/L and change to intravenous rehydration with glucose injection, adding 1 unit of insulin for every 2-4g of glucose, and also need to apply small doses of insulin intravenously to lower glucose. Also pay attention to monitor the patient’s electrolytes and actively correct other electrolyte disorders. Therefore diabetic hyperosmolar hyperglycemic syndrome has a relatively high mortality rate if it is not treated promptly and reasonably.