The invention provides a bio-adsorbent for treating dye wastewater and a preparation method therefor and application thereof and belongs to the technical field of dye wastewater treatment. The bio-adsorbent contains the raw materials in parts by weight: 35-40 parts of edible fungus waste, 22-30 parts of bamboo shoot waste, 20-25 parts of pomelo peel and 5-12 parts of tea leaves. The preparation method comprises the steps of pretreating the raw materials, then, adding aqueous alkali into the pretreated raw materials, carrying out stirring, washing an activated product with water until the activated product is neutral, drying the washed activated product, then, adding a citric acid solution to soak the activated product, carrying out heating stirring, washing a modified product with water until the modified product is neutral, drying the modified product, then, adding an alcoholic solution to soak the modified product, carrying out ultrasonic wave assisted treatment, washing a product with water until the product is neutral, and drying and crushing the product, thereby obtaining the bio-adsorbent for treating the dye wastewater. According to the application of the bio-adsorbent in the treatment of the dye wastewater, the bio-adsorbent is added into a dye aqueous solution for oscillatory reaction, and filtering separation is carried out, so as to complete adsorption removal for the dye aqueous solution. According to the bio-adsorbent for treating the dye wastewater and the preparation method therefor and the application thereof, the problem of environmental pollution is solved, the resourcing of the wastes is realized, and the aim of treating wastes with wastes is achieved.