1917 April 16, Lenin returned to Petrograd from Switzerland. The next day, at the Bolshevik meeting, Lenin published the famous Outline of April, which clearly put forward the plan and strategy for the transition from bourgeois revolution to socialist revolution. According to the situation at that time, the possibility of peaceful development of the revolution was estimated, and the slogan "All political power belongs to the Soviet Union" was put forward. April Outline is a model of Lenin's creative application of Marxist theory to solve Russian revolutionary problems. It is the concretization and new development of Lenin's socialist revolutionary theory. It has played a great guiding role in the preparation and realization of the socialist revolution by the Bolshevik Party.