Abstract: Objective To analyse the relationship between body mass index(BMI)and the incidence and radiographic progr ession of osteoar thritis(Kellgren/L awrence score,K/L score).Methods Cross-sectional and longitudinal studies were conducted to analyse the relationship between BM I and the incidence and radiographic progression of osteoarthritis.The knee osteoarthrit is analyses included 223 participants aged 30 years and older.416 controllers par ticipated in the trial.Radiographic OA was assessed using the Kellgren/L awrence(K/L)g rading system.Body mass index was measured in all participants.All participants were divided into two groups according to WHO criterion for obesity(obese group:BMI≥25,normal weight gtoup:BMI<25).Odds Ratio,95% confidence interval were calculated by compar ing BM I between two groups.Results 11,69,58,84 patients had K/L score of I~IV respectively.BM I in subjects,with KOA was significantly hig her than that in controls(P<0.0001).Simultaneoualy,there was a certain correlation between BMI and radiog raphic K OA(Pearsou coefficient=0.222,P<0.01);Obesity was a great risk for KOA(OR=2.63,95% CI=1.876-3.688,χ²=31.5,P10-7).Conclusion Obesity is a great risk for KOA;Simultaneously,it is correlated with progression of radiographic KOA.Weight control is one of the efficient ways to prevent knee osteoarthrit is.