Abstract: On the researching of covering rough sets theory,Rough-Vague sets model and its properties based on cover were researched by integrating rough sets theory and vague sets theory. In order to measured this model’s uncertainty perfectly,firstly,it measured the uncertainty of the classification capability of cover by defining knowledge capacity measure. Such method reflects the essential characteristic of knowledge classification. And then it defined Groughness to measure the model's uncertainty effectively by combining knowledge capacity and roughness(the measure of border field). The concisely and validity for this measurement were proved by analyzing example.

Key words: Vague sets, Rough-Vague sets, Knowledge capacity, Uncertainty