The invention discloses an ammonia production method and device capable of improving SCR denitration efficiency. The ammonia production device is characterized in that a cylindrical pipe barrier formed by arranging cylindrical pipes in a row is arranged at the front part of each of an upper catalyst layer and a lower catalyst layer in an SCR denitration reactor; magnesium metal powder is sprayed into the cylindrical pipes according to the set rate to form nitrogen fixation reaction in pipe cavities; N2 in smoke under a high-temperature condition reacts with magnesium metal to form Mg2N3; and NH3 generated after dissolution reaction of Mg2N3 and water is fed back to an ammonia spraying grating and reapplied to SCR denitration. N2 concentration is effectively reduced in the SCR denitration reactor; NO and NH3 reaction toward a positive direction is facilitated; and meanwhile, self-production of NH3 is achieved. The device is simple in structure and can be widely applied to an SCR reactor in a coal-fired power plant; the denitration efficiency is improved; and 'ultra-low emission' can be achieved under the condition of not adding a layer of denitration catalyst to the power plant.