The invention provides a combustion improver for a boiler. The combustion improver is prepared from the following ingredients in parts by weight: 4 parts of manganese dioxide, 4 parts of molybdenum oxide, 4 parts of ferric oxide, 4 parts of zinc oxide, 4 parts of copper oxide, 4 parts of calcium oxide, 4 parts of magnesium oxide, 4 parts of potassium oxide, 4 parts of sodium oxide, 4 parts of aluminum oxide, 16 parts of selenium dioxide, 16 parts of strontium oxide, 16 parts of oxygen difluoride, 16 parts of No.97 gasoline, 16 parts of No.20 diesel, 16 parts of ethyl alcohol, 16 parts of kerosene, 10 parts of paraffin, 10 parts of normal octane, 10 parts of nonane, 10 parts of decane, 10 parts of undecane, 10 parts of dodecane, 10 parts of eicosane, 10 parts of triacontane and 10 parts of tetracontane. The combustion improver provided by the invention has the advantages that the pollution can be reduced, the combustion efficiency is improved, and the service life of the boiler is prolonged. The invention also provides a preparation method and application of the combustion improver.