The invention provides a waste composite high-heat biomass fuel and an ultrasonic microwave assisted preparation method thereof. The waste composite high-heat biomass fuel is prepared from the following components in parts by dry weight: 25-35 parts of forestry and agricultural residues, 15-25 parts of household waste, 15-25 parts of sludge, 15-25 parts of excrement, 15-25 parts of pulverized coal, 15-25 parts of waste tire rubber particles and 2-10 parts of combustion improver; the combustion improver is composed of dolomite powder, black shale powder, serpentine powder, urea, potassium perchlorate, red mud, calcium peroxide, manganese oxide, strontium peroxide, zinc oxide, cerium oxide, boric sludge and ferrocene. The waste composite high-heat biomass fuel is suitable for long-time storage without peculiar smell. The waste composite high-heat biomass fuel is high in combustion temperature which can be within the range of 1450-1500 DEG C, and compared with a common biomass fuel, the combustion efficiency is improved by about 40%; the heat value of the waste composite high-heat biomass fuel can be within the range of 5200-5600 kilocalories/kilometer, and each ton of the waste composite high-heat biomass fuel is equivalent to 0.77 ton of standard coal; the combustion tail gas conforms to the national relevant regulations, the sulfur removal rate can be 98% and the nitrate removal rate can be 95%.