The dialectical relationship between freedom and necessity is a very important issue in Marxian theory. It involves not only the normative dimension of Marx's critique of capitalism, but also the essential provisions of communist society. The British and American academic circles have formed three typical views of “pessimism”, “optimism” and “swing theory”. Their common theoretical flaw is to regard freedom and necessity as external and opposite relations, rather than dialectical unity; The qualitative improvement of Marx's thought in the capital theory period and the solution to the harmonious unity of the relationship between freedom and necessity.