The invention discloses an integral gasification combined circulation technology (IGCC) coal gasification and desulfurization unit-based ammonia-nitrogen removing device and method. According to the device, a coal gas condensate inlet is formed in the left upper part of a stripping tower, and low-pressure steam inlet is formed in the left lower part of the stripping tower; the top nozzle of the stripping tower is connected with the upper nozzle of a stripping gas cooler through a pipeline, and the bottom nozzle of the stripping tower is connected with the inlet of a stripping water pump through a pipeline; the outlet of the stripping water pump is connected with a gasification device through a pipeline; the lower nozzle of the stripping gas cooler is connected with the left upper nozzle of a gas-liquid separation tank through a pipeline; the upper nozzle of the gas-liquid separation tank is connected with a sulfur removing and reclaiming device through an ammonia-containing acid gas pipeline; the bottom nozzle is connected with the inlet of a condensate return pump through a pipeline; and the outlet of the condensate return pump is connected with the right upper nozzle of the stripping tower through a pipeline. The device has the beneficial effects that the ammonia-nitrogen accumulation of a desulfurizing agent MDEA solution system can be reduced, the coal gasified gas desulfurizing agent MDEA solution degradation speed can be retarded, and the service cycle can be prolonged.