Currently, the phenomenon of employees' overwork in enterprises, especially for research and development (R & D) personnel, is very common and widely seen in China. And one of the key factors for their overwork is the winner-take-all market. An analysis of the prisoner's dilemma shows that in a winner-take-all market, enterprises have to bring their employees' potential, in particular the R & D personnel, to their limits. As for the R & D personnel, they are encouraged to take their initiative to work for too long hours by the winner-take-all market mechanism, and also get a sense of fulfilment from the process and results of their work. Thus, the R & D personnel's super-long work carries the nature of their active choices. Therefore, it is difficult to govern employees' overwork in a winner-take-all market. It is suggested that the government, to a certain extent, should regulate employees' overwork by limiting the intensity of market competition.