Abstract: To avoid the excessive subjectivity influenced by the conventional determination methods of weight factor, the rough set was introduced to the solution of the weight factor in the extenics evaluation. The problem of the weight factor was transformed to the evaluating of the attribute significance. The decision table was established by the rough set theory to make the knowledge reduced and determine the relevant evaluating indexes. According to the significance of evaluating indexes, the weight factor can be calculated. By comparing the weight factors figured out by the rough set theory and by the dependent function method in the practical engineering, its known that the weight factor based on rough set is more reasonable and with higher reliability.

Key words: rough set, extenics, attribute reduction, weight factor