To accurately and effectively evaluate pollution flashover condition of the in-service composite insulators that work frequently in extreme weather

a corresponding evaluation method combining rough sets and information entropy is proposed with regard to randomness

uncertainty and incompleteness of complex influencing factors. A multidimensional evaluation system of composite insulator is built to ascertain the importance of different condition attributes in the view of information entropy

and the relative weights of the attributes with rough sets theory

thus to realize quantitative expression of condition evaluation. This insulator condition evaluation method is completely based on data driving

so it can effectively avoid the subjectivity in evaluation and has proper expandability and fault tolerance. Application shows the method has excellent discrimination and is capable of reflecting real pollution flashover condition of composite insulator fleetly and accurately. This research may provide a basis for inspection and maintenance of composite insulators.