The invention relates to a high-yield 'cellulose, hemicelluloses and lignin enzyme' straw decomposition additive and a preparation method thereof. The high-yield 'cellulose, hemicelluloses and ligninenzyme' straw decomposition additive comprises the following preparation raw materials: a cellulose, hemicelluloses and lignin enzyme mixture, plant materials, sugar and urea, wherein the cellulose, hemicelluloses and lignin enzyme mixture consists of cellulase bacillus subtilis fermentation liquor, a rhizopus oryzae fermentation substance and ligninase white-rot fungi fermentation liquor; the weight ratio of the cellulase bacillus subtilis fermentation liquor to the rhizopus oryzae fermentation substance to the ligninase white-rot fungi fermentation liquor is 3-7 to 5-10 to 5-10. By adoptingthe high-yield 'cellulose, hemicelluloses and lignin enzyme' straw decomposition additive provided by the invention, different bacterial florae can harmoniously coexist and be mutually promoted, an effect of complementary advantages can be achieved, the effective viable count can be increased, the enzyme yield can be increased, cellulose, hemicelluloses and lignin in crop straw can be rapidly andeffectively decomposed, and rapid treatment and circulation of straw biomass resources can be achieved.