Abstract: Hongzhou Zhao is the founder of science of science and scientometrics in China, as well as the initial hypothesis of knowledge unit is one of his excellent achievement. The knowledge unit theory including unit capacity, knowledge entropy that proposed by Zhao is introduced systematically in memory of the founder. Further, how the knowledge unit theory has been diffused is investigated. The development tendency of knowledge unit theory promotes the new progress of research objects, research methods, management practice for science of science.