The invention discloses a wood and grass fuel for a biomass power plant and a preparation method thereof. The fuel is prepared from the following raw materials in percentage by weight: 10-30% of rice straw, 13-16% of cotton stalk, 4-10% of rice husk, 32-36% of bark, 3-10% of strain, 2-7% of leftovers, 0-9% of peanut shells and 3-6% of mulberry root; for the rice straw, the moisture content is required not to be higher than 30%, the ash content is 10-12%, and the low heat value is not lower than 10050KJ/Kg; for the cotton stalk, the moisture content is required not to be higher than 27%, the ash content is 4-10%, and the low heat value is not lower than 12400KJ/Kg; and for the rice husk, the moisture content is required not to be higher than 14%, the ash content is 11-14.5%, and the low heat value is not lower than 13200KJ/Kg; and for the bark, the moisture content is required not to be higher than 45%, the ash content is 4-10%, and the low heat value is not lower than 8000KJ/Kg. The preparation method can effectively and uniformly blend different kinds of fuels, is favorable for experimental analysis, greatly reduces experimental expenses, improves the proportion of straw fuel put into a furnace, and improves the economic benefit of biomass power generation.