The invention discloses a method for online automatic maintaining of hot-rolled laminar cooling manifolds and belongs to the technical field of automatic control. The laminar cooling manifolds are maintained by utilizing the steel rolling interval time, and therefore the service life of the laminar cooling manifolds is prolonged. Firstly, the running conditions of a laminar manifold control valve are judged; then the load carrying conditions of a finishing mill and laminar roller beds are taken into consideration, the speed of the laminar roller bed cannot be zero, in addition, according to the method, running needs to be conducted in an automatic mode, and a rolling mill secondary CTC model does not have starting and stopping orders on the laminar manifolds; and finally, and an operator controls whether the function is started or not and controls the maintaining time. The method has the beneficial effects that surface cooling of the laminar roller beds can be more uniform, and meanwhile the damage rate of the electromagnetic valve can be reduced; and especially, the service life of the laminar headers can be prolonged, and the equipment maintaining cost is saved.