Abstract: Objective To explore the synergistic effect of diabetes family history and obesity on the incidence of type 2 diabetes.Methods Totally 450 type 2 diabetes patients were appointed as case group and 3 158 people with normal blood glucose were appointed as control group.The interaction between diabetes family history and obesity was analysed with an additive model.Results There was a synergistic effect between diabetes family history and obesity on the incidence of type 2 diabetes.The synergy index was 1.655.The relative excess risk due to interaction was 0.834 and the pure attributable interaction percent was 39.58%.After adjusting for age,gender,hypertension,physical activity,income,and education by multiple logistic regression,the synergy index was 1.710; the relative excess risk due to interaction was 1.047; pure attributable interaction percent was 41.51%.Conclusion Individuals with both diabetes family history and obesity have a higher risk of type 2 diabetes compared to those exposed to only one factor.