"Knowledge is power" is a slogan that we are familiar with in twenty-first century. It is also an important idea for us to realize self-breakthrough in the era of knowledge economy. This paper traces the historical changes of the concept of "knowledge", analyzes the different forms of the different times, combined with Xi Jinping for the important role of knowledge and talent, further explains "knowledge is power" in the ancient times, modern times and modern three ontology of the connotation and its unique value in the modern era