Abstract: The case base maintenance is the core of case-based reasoning(CBR).There are still some shortages in current related researches.In this paper,for mechanical product design,a case base maintenance method based on fuzzy-rough set is put forward.Firstly,the case feature weight calculation,case base family partition,case feature reduction of product design cases are discussed.Secondly,the concepts of coverage and reach-ability are introduced to filter typical cases in the case base.Finally,a case base maintenance system for construction machines is developed,and an example is given to show the system's effect.