The invention relates to a condensing system for heating heat-supply hot water with heat of waste steam from a steam turbine, which comprises a generator (1), a steam turbine (2) and a direct air-cooling system, wherein the direct air-cooling system comprises an air-cooling blow-off pipeline (3), an upper valve (4) in the air-cooling blow-off pipeline, an air cooling condenser (5), an air-coolingblower (6), an air-cooling condensed water pipeline (7), an upper valve (8) in the air-cooling condensed water pipeline, an air-cooling vacuum-pumping pipeline (9), a vacuum-pumping device (10) and acondensed water collecting device (16). The air-cooling blow-off pipeline (3) of the direct air-cooling system is parallelly provided with a moisture heat exchanger system; the moisture heat exchangersystem comprises a moisture heat exchanger (11), a condensate pipeline (12) of the moisture heat exchanger, an upper valve (13) in condensate pipeline of the moisture heat exchanger, a steam feed pipeline (14) of the moisture heat exchanger, an upper valve (15) in the steam feed pipeline of the moisture heat exchanger and a vacuum-pumping pipeline (17) of the moisture heat exchanger. The condensing system reduces the energy waste generated during the direct discharge of the heat of the waste steam into atmosphere from the air through heat exchange, improves the energy utilization and reducesatmosphere thermal pollution.