Basing upon the nature of man to seek ideal and knowledge, the paper discusses the internal relation between seeking ideal and seeking knowledge, and emphasizes that it is knowledge that provides man with the real power to realize his ideal. From the viewpoint of objective cognition, the paper analyses the knowledge essence of objectivity, and therefore proves the grounds of which knowledge is power. Possessing knowledge, man can not only own matter as the object of knowledge in mind, but also strengthen his control and creative capacity in action, and according to his ideal, enhance more possibility to utilize things and create object practically .If man would give full play to the knowledge power, the paper holds, he must apply knowledge to practice, and transform the knowledge power into the practice power, meanwhile, make practice onto the action of knowledge. The paper points out the actual ways and forms for transforming the knowledge power onto the practice power. Lastly, the paper emphasizes that knowledge, as tremendous and constructive power, should guarantee the existence and development for society and man. Therefor,the knowledge power and its use should have the character of integrating Li and Ren.