A method and an intermediate for preparing a tulathromycin. The method includes the following step: in an organic solvent, subjecting a compound represented by formula (II) and an n-propylamine to a ring-opening addition shown below to obtain a tulathromycin represented by formula (I), wherein the organic solvent is a 1,2-propandiol. Tulathromycin obtained using the method has a high purity, with an HPLC purity being 95% and above, and up to 99% and above, satisfying a required purity for preparing a tulathromycin as a pharmaceutical formulation. The method has a high yield, is simple to operate, and is more suitable for industrial production.