This paper describes the contamination performance of outer-rib type suspension insulators with multi-sheds. The various evaluation tests, such as field exposure tests, aerodynamic analysis of wind flow around the specimen insulators by computer aided engineering and artificial contamination withstand voltage test, were carried out. Analysis of contamination degree and fog withstand voltage test were also carried out on the removed insulators from a 500 kV line. As the results, outer-rib type insulators have superior contamination performance especially under accumulation contamination conditions in China.