Abstract: The moral theory of Marx and Engels affirms the dynamic and practical characteristic of human beings as moral subjects. It clarifies the dominant role of productive labor and material benefits on morality， completes the theoretical criticism of ideological “moral theory”， and reserves the theoretical space for moral constructivism. At the same time， it describes a rigorous system which takes the realistic individual as the subject， the action and construction of morality as the procedure， and the “real person's morality” as the goal. It shows the essential characteristics of the moral constructivism. Because of the misreading of the theoretical form of constructivism in the moral theory of Marx and Engels， there has been a simple emphasis on the moral deconstruction of the moral theory of Marx and Engels， ignoring its moral construction significance， or vice versa， which has fueled to boost the thoughts of “ethical socialism” and “anti-moralism of Marx and Engels”， making them the two theoretical errors in people's scientific understanding of the moral theory of Marx and Engels.

Key words: moral theory of Marx and Engels, moral constructivism, ethical socialism, anti-moralism