To derive the negative rules from the incomplete decision information system, the concept of negative support set
of descriptors is proposed. The lower and upper approximations based on such negative support set are presented, and their
properties are discussed. Moreover, the approach to acquire the certain and credible negative rules by the proposed lower
and upper approximate is presented. For facilitate application, an approach of discernibility matrix is proposed to obtain the
reduction, and the results of the illustrative examples show the effectiveness of the approach.