The invention relates to the field of industrial waste gas purification, environmental protection and energy, and specifically relates to a system and method for relieving blockage of an air preheaterthrough catalytic oxidation of escaping ammonia. The system comprises a boiler and a chimney, wherein the boiler is connected with the chimney through a flue; an air inlet channel is further formed in the boiler; and the flue is connected with the air inlet channel through the air preheater. The system is simple in structure, ozone is sprayed into the flue through an ozone spraying device, a catalyst layer is combined, the ozone and the escaping ammonia in flue gas are removed, the amount of the sprayed ozone is that the molar ratio of the escaping ammonia in the flue gas located between an SCR denitration reactor and the catalyst layer is more than or equal to 3, the thoroughness of escaping ammonia removal is guaranteed, and therefore the escaping ammonia is efficiently removed, the pressure difference of the air preheater is prevented from being increased, and blockage of the air preheater is effectively relieved.