The invention discloses a method for coating fire coal fly ash with nanoparticles, and belongs to the technical field of ash deposition prevention and control. According to surface tension gradient generated by component concentration difference generated by contact of coal-fired fly ash and nano-particles with different properties, the Marangoni effect is further caused, the movement direction of the nano-particles in the coal-fired fly ash is changed, the direction and strength of Marangoni convection are adjusted, rotational flow impact is carried out by oppositely and simultaneously spraying in the tangential direction of the high-temperature impinging stream reactor, so that the coal-fired fly ash is uniformly coated with the nano-particles. By adopting the method disclosed by the invention, the quality of a coating product can be enhanced, the structure and composition of the fly ash deposition layer are regulated and controlled by utilizing the Marangoni effect, further the viscosity of the coal-fired fly ash is effectively reduced, the deposition of the fly ash is inhibited, the influence of the formation and deposition of the fly ash on the overall system efficiency is reduced, and the method has great significance in prolonging the service life of a boiler, improving the power generation efficiency of the boiler and expanding the application field of fire coal.