With the increase of obese children, harmfulness of obesity to their health was studied to lay a basis for formulating corresponding intervention measures. Blood sugar, intelligent quotient (IQ), thyroid function, cardiac and pulmonary function, and index of gonad development were determined in 150 obese children and 150 normal healthy children. Results showed baseline secretion of insulin and C-polypeptide in obese children were significantly higher than that in controls, and thyroid function, total IQ, speech IQ and operation IQ all were relatively lower, cardiac and pulmonary function was significantly lower, and gonad development and maturity took place earlier in the former than in those in the latter. It indicated that there were a lot of risk factors harmful to their health in obese children.