The invention relates to cofferdam filling construction, and discloses a rapid cofferdam filling construction method for a pit in a pit. The rapid cofferdam filling construction method includes the steps that a cofferdam device is manufactured; a frame is welded through reinforcements to be in the specification slightly larger than that of the pit in the pit; then a dense-mesh steel plate mesh and a connecting water collecting well are paved on the periphery of the frame, and a steel tube or a structural steel support is used inside the frame; the pit in the pit is excavated, wherein the pit in the pit is excavated at the place where the elevation needs to be adjusted; the cofferdam device is installed and adjusted, after excavation of the pit in the pit is finished, the cofferdam device is instantly placed into the excavated pit, and the cofferdam device is adjusted along with resetting of soil flow or drift sand; after adjustment is finished, concrete is poured on the periphery of the cofferdam device, a water pump is installed in the water collecting well for water pumping after the concrete solidifies, a water isolation mold, a pouring pad layer, the assembling reinforcements, a formwork and the pouring concert are paved to the bottom of the cofferdam device after the water level falls, and then construction can be completed. By means of the rapid cofferdam filling construction method, the containment effect is stable, and the overall schedule of construction of the pit in the pit is guaranteed; influences on the peripheral construction environment of the pit in the pit are avoided.