A method for preparing high-temperature, active particle-containing steam. The method includes: 1) preparing steam; selecting one or several non-oxidizing gases as a working gas; ionizing the working gas into a plasma working medium by using a plasma generator; and 2) injecting the plasma working medium into a high-temperature steam generator to form high-temperature ionized environment while introducing the steam into the high-temperature steam generator for allowing the steam to contact with the plasma working medium so that the steam is heated and activated to form active particle-containing steam. A device for preparing the high-temperature, active particle-containing steam is also provided.