Trough combining evolutionary epistemology theory with biological evolution theory, this paper presents a knowledge evolution algorithm. The basic principle and realizing ways is also given. The evaluating function of the knowledge is created too. When the algorithm is used in the evaluation of the reader's satisfaction in a library, we can obtain successful experiment results. The experiment shows that the knowledge evolution algorithm can promote both the quantity and the quality of the knowledge, which is an effective assistant means to make a correct decision.