Socialism: Utopian and Scientific is the theoretical achievement that Engels positively responded to the theoretical and practical challenges facing scientific socialism in 19th century. In order to deal with the misunderstandings and meet the practical challenges to scientific socialism, Engels reinterpreted scientific socialism with logic of science and value. In the process of analyzing and criticizing capitalist society, Engels once again revealed inevitable extinction of capitalism, elaborated the approach of the proletariat’s revolutionary movement, emphasized the importance of proletariat’s dictatorship and provided scientific guidance for the proletariat revolution. In the times of big world change within the recent hundred years, to re-examine Engels’ defense and development of scientific socialism is of great significance and enlightenment for clarifying the wrong understanding of socialism, and strengthening our confidence in the path of socialism with Chinese characteristics.