A compartment method for large-volume bottom seal of a steel boxed cofferdam and a steel boxed cofferdam structure relate to the technical field of bridge construction. Specifically, the cofferdam hasa plurality of steel protection cylinders therein. The method includes the following steps: disposing, on the inner wall of a cofferdam side plate, multiple pairs of vertical slide paths, wherein each pair of slide paths is relatively positioned in the same plane, and lowing a cofferdam body; producing multiple plate bodies matching the respective pairs of slide paths, lowing each plate body to below the ground along each pair of slide path, and dividing the cofferdam body into multiple construction areas; setting the construction order of the multiple construction areas, and setting the positions of adjustable pads abutted against the respective plate bodies according to the construction order, in order that in the construction areas on both sides of each plate body, the adjustable padsare installed between the steel protection cylinder and the plate body in the construction area where construction is executed later. The method reduces the difficulty in lowering the cofferdam, and the compartment with single-wall structure is easy to machine and economical.