The invention relates to a special oil filtering device for a steam turbine and an oil filtering method. The oil filtering device is mainly used for treating the turbine oil of a generator set and canquickly and effectively remove moisture, gas and impurities in the oil. The oil filtering device comprises a water tank (1), a vacuum tank (2), a heater (3), a condenser (4) and a vacuum pump (5), wherein the water tank is connected with the vacuum pump through a water pipe; the top of the vacuum pump is connected with the condenser through an air inlet pipe (6); the side surface of the vacuum pump is connected with the condenser through a condenser discharging pipe (7), the bottom of the condenser is provided with a water storage tank (8), the lower part of the water storage tank is connected with an air discharging pipe (9) and a water discharging pipe, the upper part of the condenser is connected with the vacuum tank through a pipeline, a vacuum meter (11) is arranged on the pipeline,the invention relates to the oil filtering device of the steam turbine.