Abstract： Objective To explore the difference of four calculating methods used to determine the obesity. Methods Two thousand four hundred and forty six (2446) men and three hundred and seventy nine (379) women were measured height and body mass, Standard body mass, BMI, body fat ratio and obesity index(OI) were calculated with formula. According to the BMI≥ 25 kg/m2 , BMI ≥ 27 kg/m2 and BMI≥28 kg/m2, the obese adults were 1419,680 and 435 respectively;there were 649 adults that their body mass was over 20％standard body mass; there were 639 adults that their body fat ratio was over 25％(male)and 33％(female). Results For obesity determination, the adults who were 20％overweight and over standard body fat ratio were significantly different from those whose BMI were over 25 kg/m2 ( P＜0. 05 ) ;Those who were 20％overweight and over standard body fat ratio were not significantly different from those whose BMI were over 27 kg/m2 ( P＞0.05 ) ; Those who were 20％overweight and over standard body fat ratio were significantly different from those whose BMI were over 28 kg/m2 ( P＜0. 05 ). Conclusion Determining obesity with BMI≥27 kg/m2 is feasible and rational.