In Case-Based Reasoning (CBR), the determination of the weights of case characteristics is the base of the accurate case match, even influences the CBR execution. The current methods of determining the weights of case characteristics include subjective and objective weighting method but, some defects exist in them. In order to decrease subjectivity and increase objectivity of weight determining, the paper presented a new kind of combination weighting method that is the combination of the Analytic Hierarchy Process (AHP) with roughness set theory. The weighting process about AHP, roughness set theory, and combination method was described in detail respectively. An example was given to verify the effectiveness and accuracy of the combination weighting method.