The low nitrogen condensing integrated steam boiler has more condensing waste heat recovery devices than the traditional gas boiler, which can heat cold water by absorbing high temperature flue gas waste heat, thus consolidating thermal efficiency. When the condensing integrated steam boiler is running, a large amount of high temperature flue gas is reduced by the condenser during the discharge process. The boiler furnace bile adopts full corrugated structure, which increases the radiation and convective heat transfer area. The furnace bile expands freely after being exposed to high temperature radiation. The front smoke box door adopts split design, so that the smoke box does not run smoke and does not leak smoke, which is easy to maintain. The multi-return design of flue gas ladder enables the high temperature flue gas to carry out radiation heat transfer along the corrugated furnace, convective heat transfer in the threaded flue pipe and condenser, and discharge into the atmosphere through the chimney, and the thermal efficiency of the boiler is consolidated.