NOVELTY - Preparing hydrogen by metallic nanoparticles comprises using vibration roll pressing method for manufacturing single-crystal nanostructure. Process and manufacture of nanoparticles is done on roll pressing vibration grinding machine; metallic nanoparticles undergo chemical reaction at below 250 degrees C to prepare hydrogen and collecting it into the hydrogen collector. Crude particles can be discharged from lower part of rotating flow field reactor. Metal oxide can be collected by static electric dust remover. Noble gas can be recycled.    USE - The method is useful for preparing hydrogen by metallic nanoparticles (claimed).    ADVANTAGE - The method has low energy consumption, high hydrogen preparing rate, and no pollution.    DETAILED DESCRIPTION - Preparing hydrogen by metallic nanoparticles comprises using vibration roll pressing method for manufacturing single-crystal nanostructure. The process and manufacture of nanoparticles is done on roll pressing vibration grinding machine; the metallic nanoparticles that are less than 10 nm and steam can be brought into the rotating flow field reactor by noble gas and then perform chemical reaction at below 250 degrees C, preparing hydrogen and collecting it into the hydrogen collector. Crude particles can be discharged from lower part of rotating flow field reactor. Metal oxide can be collected by static electric dust remover. Noble gas can be recycled. An INDEPENDENT CLAIM is included for a device for preparing hydrogen by metallic nanoparticles comprising rotating flow field reactor with insulating layer, condenser, hydrogen collector, drier, static electric dust remover, and draught fan, where upper part of the rotating flow field reactor is pole and lower part is cone; machine wall of the rotating flow field reactor is opened with the metallic nanoparticles inlet and the steam inlet; bottom of cone is opened with the crude particle outlet; double-layer tube is connected at center of top part of the pole; inner tube of double-layer tube is hydrogen outlet tube; outer tube of the double-layer tube is metal oxide and noble gas outlet tube; inner tube of double-layer tube connects with the condenser and hydrogen collector in series in turn through the pipeline by valve; outer tube of the double-layer tube connects with the condenser, hydrogen collector, drier, static electric dust remover and draught fan and the metallic nanoparticles inlet through pipeline by valve.    DESCRIPTION OF DRAWING(S) - The drawing shows the schematic view of the device used for preparing hydrogen by metallic nanoparticles.