Since 1990s, communication scholars began to self-reflect the construction of their disciplinary history and criticize traditional intellectual history and biographical history writing. Based on sociology of knowledge, this study adopts both internal and external perspective to re-examines the social background and academic diffusion of knowledge Gap Hypothesis during 1970s. This study finds that the birth of knowledge Gap Hypothesis is embedded in theGreat Society Plan and relevant education studies during 1960s. Besides, the development of knowledge Gap Hypothesis as a research agenda is assisted by both the efforts of Minnesota team and various scholars from land-grant universities in northern agricultural states. The significance of this study is to advocate an investigation of history of communication studies using sociology of knowledge.