Engels's scientific atheism is the scientific view of religion in the first half of the nineteenth century. The process of its formation and establishment is interwoven with Engels's reflections of previous religious beliefs and various religious theories. Engels's scientific atheism illustrates religious phenomena and its derived essence which is the reflection of the external forces that govern the daily life of people in their minds. It also establishes the adversarial relationship between science and religion, criticizes religious mysticism and the theory of spiritualism based on the consistency between science and atheism, clarifies the difference between communism and religious principles and gives the demonstration of atheism for scientific socialism. Engels makes outstanding contributions to the development of the scientific atheism of Marx and advocates Marx's scientific atheism in a scientific way. Engels expounds the evolution of religion from different angles, makes the detailed division of religious development available for the first time, deepens the study of Marxism scientific atheism and enriches Marx's scientific atheism in the relationship between religion and socialism. Therefore, Engels' scientific atheism is of great importance for China to uphold and develop socialism with Chinese characteristics today.