The invention provides a preparation method of burn-free tourmaline biological ceramsite and an application thereof in decolouration of dye wastewater. The preparation method disclosed by the invention comprises the following steps: (1), weighing the following components according to a formula: 37.5-46.5% of coal ash, 12-17% of cement, 12-17% of lime powder, 12-17% of sodium bicarbonate, 1-2% of gypsum, 3-7% of water glass, 1-10% of tourmaline, and 0.5-2% of aspergillus fumigatus, wherein the sum of the percentages by weight of various components is 100%; (2), granulating: uniformly mixing various components to form a mixture, adding water into the mixture, wherein the addition amount of water is 30-40% of that of the mixture; uniformly stirring, and granulating to obtain raw ceramsite with the particle size of 3-8 mm; and (3), aging, drying and steaming the raw ceramsite at constant temperature to obtain the burn-free tourmaline biological ceramsite. The burn-free tourmaline biological ceramsite prepared by the preparation method provided by the invention has the characteristics of being low in cost and good in decolouration property.