The invention relating to the branch of material thermal treatment technology discloses a method of extending an after-rolling on-line quenching cooling space to the cooling table.According to the invention, a quenching cooling cover for rolled steel is designed at a reserved space between a finishing mill and a cooling table, a quenching cooling interval length of the cooling table is determinedaccording to the requirements of the velocity of movement of the roll table and the quenching time, the quenching cooling interval of the cooling table is divided into at least one quenching cooling cover of the cooling table, one or more quenching cooling covers of the cooling table are provided between each two roll tables, at the same time that rolled steel moving on the cooling table is stopped, a control system stops the water-spraying of the quenching cooling covers on the cooling table one by one according to a sequence direction opposite to the moving direction of the rolled steel andthe moving speed of the rolled steel after precision rolling, therefore, cooling times of all the parts in the length direction of the rolled steels are accordant.According to the invention, problemsthat a reserved space between a finishing mill and a cooling table is skimpy and the quenching and cooling of each part of the rolled steels on the cooling table is not uniform are both solved.