Taking the law of unity of opposites as the core, this paper expounds the fundamental opposition between metaphysical development view and dialectical development view, explains the dialectical relationship between objectivity and universality of contradiction, identity and struggle of contradiction, emphatically expounds the dialectics of knowledge, and analyzes the dialectical relationship between absolute and relative, abstract and concrete, general and individual philosophical categories, as well as the epistemological root of idealism. The proposition of dialectics is also a famous conclusion of Marxist epistemology. This paper is an outstanding performance of Lenin's research on dialectics theory. It supplements and deepens the thought of the article Principles of Dialectics, enriches and develops materialist dialectics, and occupies an extremely important position in the history of Marxist dialectics.