An incremental target recognition algorithm based on improved discernibility matrix in rough set theory is presented. We compare the new approach with our previous nonincremental algorithm in detail, especially analyze the temporal complexities of these two algorithms. Some comparable experiments have been completed in our "Information Fusion System for Communication Interception Information (IFS/CI/sup 2/)". Experiment results show that the new algorithm is more efficient than the previous while the recognition ratio is satisfying.