Abstract: Uncertainty measure is one of the basic problems of rough sets theory.The uncertainty of rough fuzzy sets is caused by both the roughness of the difference of the upper and lower approximate sets and the fuzziness of the uncertain concept extension.Now the uncertainty research on rough fuzzy sets is not yet well understood.This paper discussed the uncertainty of rough fuzzy sets in covering approximation space,proposed the more strict revised measurement criterion,and brought out the revised roughness by the membership difference among the original fuzzy sets,the upper and lower approximation sets.Example analysis shows the measurement approach can describe the actual problems more accurately.

Key words: Covering approximation space,Rough fuzzy sets,Roughness,Rough entropy,Uncertainty