The normal range of weight for 80 years old is recommended to be equalized using BMI to assess the weight status of the elderly, to detect problems in time and give timely symptomatic conditioning or treatment to promote good health. BMI is mainly calculated by dividing weight (in kilograms) by the square of height. In general, the 80-year-old BMI value of 18.5-23.9 kg/m2 for the standard weight range, when the BMI value is less than 18.5 kg/m2 belongs to the underweight, when the BMI value of 24-28 kg/m2 belongs to the overweight, when the BMI value of more than 28 kg/m2 for obesity. When the BMI value exceeds 28 kg/m2, it is regarded as obese. 80-year-old people with too low or too high BMI values are abnormal and unhealthy. Low BMI is often seen in the elderly malnutrition, anemia, cachexia and other diseases; BMI value is too high to consider, for example, overweight or obesity, increasing the risk of cardiovascular and cerebrovascular diseases and diabetes and other diseases in the elderly. Once the 80-year-old man appeared abnormal situation, need to find the cause in time, as soon as possible to implement symptomatic conditioning or treatment, to avoid affecting the health of the elderly.