The invention belongs to the technical field of biomass gasification cofiring power generation, and particularly relates to a biomass gas cooling system. The system comprises a fuel gas heat exchangedevice and a deoxidizing device. The system also comprises a gas heat exchange pipeline arranged in the fuel gas heat exchange device; a deoxidizing device internally provided with a deoxidizing watertank, and provided with a second liquid inlet and a second liquid outlet, wherein the second liquid outlet of the deoxidizing device is connected with a first liquid inlet of the fuel gas heat exchange pipeline through a first pipeline, and the second liquid inlet of the deoxidizing device is connected with a first liquid outlet of the fuel gas heat exchange pipeline through a second pipeline. According to the biomass gas cooling system provided by the invention, the complex mode that media such as heat conduction oil are adopted as an intermediate carrier at present is solved, and the purposes of efficient cooling and no tar condensation blockage are achieved.