Different types and stages of diabetes have different appearances; the milder ones can be senseless or the more severe ones can affect life; they can be typical symptoms or non-specific and seemingly difficult to associate with diabetes. The typical symptoms are polyuria, polydipsia, polyphagia and weight loss, which should occur in this order according to the mechanism of occurrence, but can also highlight only one symptom. Polyuria: Not only does the frequency of urination increase, but also the volume of urine increases significantly, up to 20 times in 24 hours, with a volume of 2-3 liters or even 10 liters. The urine is foamy and the urine stains are white and sticky. Polyuria is due to the increase in blood sugar, exceeding the renal sugar threshold, (8.9-10 mmol/l), and the increase in sugar excreted into the urine, so the number and volume of urine increases. Polydipsia: After urinating more, the water in the body decreases, causing excitation of the thirst center of the brain and the desire to drink. It should be noted that the diagnostic criteria for diabetes mellitus are significantly lower than the renal sugar threshold, so diabetes mellitus may be diagnosed before polyuria occurs. On the other hand, the renal vascular sclerosis in the elderly increases the renal glucose threshold, so the blood glucose is very high and there is no sugar in the urine, so polyuria does not occur: furthermore, the central nerve receptors are weakened in the elderly, so despite the obvious loss of water in the body, the thirst center does not feel it and does not think of drinking, which is the reason for the non-ketotic hyperosmolar coma of diabetes mellitus, which is common in the elderly and has a high mortality rate. Excessive eating: Since blood sugar cannot enter the cells and cannot be used by the cells, it stimulates the hunger center of the brain to be excited and eat more, and there is no feeling of satiety after eating, resulting in a significant increase in both the number of times and the amount of food eaten. It should be noted that in the early stage of type 2 diabetes, due to hyperinsulinemia, the utilization of blood glucose is accelerated, and there is obvious hunger before meals, and even hypoglycemia, which is often the first symptom of type 2 diabetes. Wasting: Reduced glucose utilization, increased fat decomposition, insufficient protein synthesis, and accelerated decomposition cause wasting, such as polyuria and water loss in the body will aggravate the wasting symptoms. Similarly, the longer the duration of the disease, the higher the blood glucose: the more severe the disease, the more obvious the wasting will be.