The invention relates to a novel method for preparing tulathromycin. The method includes the steps that 3,4-acetonylidene protected demethylazithromycin is used as a starting material, a 2-hydroxyl group is firstly protected, then a 4-hydroxyl group is oxidized to a carbonyl group under Swern conditions, TMSCN is used for performing a cyano group addition reaction on the carbonyl group under the action of TBAF, a resulting intermediate compound is subjected to a hydrogenation reaction in the presence of HOAc with Pd/C as a catalyst, the cyano group in the compound is converted into an amine methyl group while a 2-hydroxy group protecting group and 3,4-acetonylidene protection are removed, and finally under the action of base, an amine methyl compound is reacted with 1-halogenated propane to achieve the preparation of tulathromycin.