Abstract: A field of environmental protection and discloses a method for preparing an amorphous silica-alumina encapsulated metal oxide catalyst and application thereof. The catalyst is prepared by filling silica-alumina precursors in tunnels of a monometallic or bimetallic complex and then performing heat treatment. The catalyst has the advantages that acidic sites and oxygen vacancies are highly dispersed, the pore size range is large and the mass transfer efficiency is high, improves the efficiency of a cracking-oxidation tandem reaction, and achieves full purification of carbon/nitrogen pollutants in landfill leachate. The COD removal rate of the landfill leachate reaches 98.3% or above, and the ammonia nitrogen removal rate thereof reaches 98.0% or above. The COD concentration of oxypyrolysis purified effluent is less than 98.7 mg/L and the ammonia nitrogen concentration thereof is less than 24.9 mg/L.