The invention discloses a method for coproducing methylbenzoic acid, methyl benzonitrie and phthalonitrile. The method comprises the following steps: (1) continuously introducing xylol, a catalyst andoxygen-containing gas into an oxidation reactor and reacting to obtain an oxidation reaction solution; (2) conveying the oxidation reaction solution into a primary evaporation tower and carrying outrectification separation; when the content of methylbenzyl alcohol in a tower kettle solution of the primary evaporation tower reaches 0.01 to 0.15 weight percent, stopping rectification, so as to obtain a low-boiling-point component and the tower kettle solution of the primary evaporation tower; (3) conveying the tower kettle solution of the primary evaporation tower into a rectification tower and carrying out rectification; when the content of the methylbenzoic acid in a tower kettle solution of the rectification tower reaches 30 to 90 weight percent, stopping rectification, so as to obtaina methylbenzoic acid product and the tower kettle solution of the rectification tower; (4) mixing the tower kettle solution of the rectification tower and ammonia to obtain a nitrile-containing reaction solution; (5) carrying out rectification separation on the nitrile-containing reaction solution to obtain methyl benzonitrie and phthalonitrile products. The method disclosed by the invention has the advantages of simple technology, few equipment investment, greenness and environment protection and good comprehensive economic benefits.