The invention discloses wheat straw biochar fertilizer promoting roots to grow and a preparation method thereof. The wheat straw biochar fertilizer promoting roots to grow is prepared from, by weight, 40-50 parts of buckwheat husks, 13-16 parts of marsh gas liquid and diatomaceous earth, 10-14 parts of ammonium nitrate, 5-7 parts of potassium chloride, 28-32 parts of turnip residues, 110-120 parts of nickel sulfate and fresh enteromorpha, 5-7 parts of compound microorganism bacterium agents, 200-220 parts of wheat straw, 18-20 parts of fresh urine and an appropriate amount of water. According to the wheat straw biochar fertilizer, soil permeability is improved through the diatomaceous earth, the turnip residues and other leavening, and the absorbing capacity of crop roots is enhanced through the marsh gas liquid and the like; by adding various compound bacterium agents, the number and the population diversity of the wheat straw biochar fertilizer are increased under the action of wheat biochar, the root growth environment is improved due to enhancement of the activity of the wheat straw biochar fertilizer, and therefore root growth is promoted easily.