The preparation process for o-ethoxy benzoic acid, a key intermediate for sildenafil, was improved with methylsalicylate. Sodium salt of methylsalicylate was firstly prepared and treated with ethyl bromide to give methyl o-ethoxybenzoate, which was hydrolyzed to afford o-ethoxy benzoic acid (HPLC purity 99.88%). The overall yield was 89.5% and It has been produced in Chongqing Kangerwei phamaceutical Co. Ltd.