Abstract: Freedom is an important clue through Marx’s thoughts, and free labor is the sign of human emancipation and individual freedom. Marx’s thoughts on free labor can be traced back to the concept of “self-activity”. The concept of “self-activity” is not only a transcendence of Hegel’s “self-consciousness”, but also a renunciation of Hess’s “free action”, which denies purely mental activities and ethical value. In Marx’s period of practical materialism, “self-activity” appeared as a critique of alienated labor, which is an affirmative of the class nature of the human beings. After Marx established historical materialism, the concept of “self-activity” began to be associated with the contradictory movement of the productive forces and production relations, which laid a foundation for Marx’s formal entry into the critique of political economy and his further study of free labor.