The invention discloses a process for preparing an intermediate of zafirlukast, and the compound is an important intermediate for preparing the leukotriene antagonist drug zafirlukast. With (5-nitro-1-toluenesulfonyl-1H-indol-3-yl) methyl acetate and 3-methoxybenzoic acid methyl ester as raw materials, under the action of acidified montmorillonite, in an inert solvent In, heat the reaction until the raw materials disappear, filter to obtain 3-methoxy-4-[(5-nitro-1-toluenesulfonyl-1H-indol-3-yl) methyl] methyl benzoate; the above compound Under alkaline conditions, hydrolysis yields the target product. The invention provides a new process route for synthesizing an important intermediate of zafirlukast, which has the technical advantages of simple operation, low reaction cost, high product yield and environmental friendliness, and can meet the demand for large-scale production of pharmaceutical products.