Abstract: the“996 phenomenon”is triggered by the speed of productivity development in the process of China's rapid economic development, while ignoring the legitimate rights and interests of workers. The discussion about the “996 phenomenon” reflects the different understandings of fairness and efficiency in the socialist market economy. The“996 phenomenon” is an intricate issue and must overcome it. So China can achieve higher quality development in the process of modernization. Marx put forward the theory of working day in Capital, in which clearly defined the boundaries of working days and effective ways to solve unreasonable working days.

Key words: Marx, Theory of Working day , “996 phenomenon”