The invention relates to a device for separating hydrogen out of superheated steam. The device comprises a left side flask and a right side flask. A three-way cock valve is installed between an opening in the upper portion of the left side flask and an opening in the upper portion of the right side flask. A lower opening of the left side flask and a lower opening of the right side flask are each fixedly provided with a rubber plug with a rubber pipe. A pipe clip is installed on the rubber pipe of the lower opening of the right side flask. A condensation water tank is placed on the left side of the left side flask and internally provided with a water pump. The water outlet of the water pump is communicated with the lower portion of the left side flask through a reducing pipe. A sampling rubber pipe is installed on the opening of the upper portion of the right side of the right side flask. A sampling injector is arranged beside the sampling rubber pipe. Hydrogen contained in the superheated steam generated by a boiler pressure vessel can be separated out, then the separated-out hydrogen is accurately measured by means of a laboratory chromatograph, the corrosion state of the boiler pressure vessel is accurately judged, and data support is provided for protection of the boiler pressure vessel.