The invention discloses a temperature control system for reducing the size difference between the head and the tail of a reinforcing bar and an operation method. A pre-water penetration system, a pipeline and a control system are improved, so that the non-water penetration function of the head and the tail of a rolled piece is realized, and the effects that the steel temperature of the head and the tail of rolled steel is higher than that of the middle, the deformation resistance is reduced, the rolling is smoothly performed and the size difference between the head and the tail is reduced are achieved.