With the development of science and technology, knowledge has become one of the key factors for enterprises in gaining competition advantages. Therefore, the study on the characteristics of knowledge dissemination within an organization will facilitate the organization to manage knowledge effectively. Based upon the research on the characteristics of knowledge dissemination, this paper puts forward a new perspective of sorting knowledge: the long-term knowledge and the short-term knowledge. Furthermore, this paper sets up a system dynamic model of knowledge dissemination within an organization and makes necessary analysis. Meanwhile, the threshold condition is presented to judge whether knowledge can be disseminated freely within an organization. According to the outcome of the analysis, management methods aiming at the two kinds of knowledge are also suggested.