The invention relates to the technical field of biochemical separation and purification, in particular to a preparation method for a tea-leaf dietary fibre. The preparation method comprises the following steps: firstly, mixing edible alcohol with a certain volume fraction and sodium hydroxide solution to prepare a first mixed solution, wherein the edible alcohol and the sodium hydroxide are in thevolume ratio of 1 to (0.5 to 2.5), and adding the first mixed solution into tea leaves according to the solid-liquid ratio of 1 to (5 to 30) for extracting the tea leaves; secondly, filtering the extracted tea leaves to obtain first filter residue, washing the filter residue with water until the pH is neutral,and mixing the edible alcohol with the certain volume fraction, hydrogen peroxide and water to prepare a second mixed solution, wherein the edible alcohol, the hydrogen peroxide and the water are in the volume ratio of (2 to 4) to 1 to 1 to (1 to 5), adding the second mixed solution intothe first filter residue according to the solid-liquid ratio of 1 to (5 to 15) for decolorizing, and filtering to obtain filter residue, wherein the filter residue is the insoluble dietary fibre. Theinsoluble dietary fibre prepared by the preparation method is high in production efficiency; the yield is greater than or equal to 20 percent; the water-retaining capacity of the product is greater than or equal to 8 g/g; the swelling force is greater than or equal to 10 mL/g.