The invention discloses a novel method for preparing a high-purity asthma treatment drug pranlukast, and relates to the technical field of organic synthesis of drugs. The method comprises the following steps: carrying out neutralization and a salt forming reaction on a reaction raw material 8-amino-4-oxo-2-tetrazole-5-yl-4H-1-benzopyran hydrochloride and an alkaline substance to generate an intermediate, and carrying out an amidation reaction on the obtained intermediate and p-phenylbutoxybenzoyl chloride in a non-polar solvent to prepare the pranlukast. The whole process of the method is simple and clean, is easy to control, allows the purity of the obtained crude product to reach 99% or above, and allows the purity of a one-time purified product to reach 99.9% or more.