Abstract: The dibutyl phthalate was take in the maleic anhydride production process as solvent. After a period of time use，in which can produce the tar high polymer. It can affect the solvent efficiency. In this method, the solvent sample after vacuum distillation was concentrated. Adding the succinonitrile,　the phthalic anhydride and the dibutyl phthalate quality percentage were deterred in the gas chromatograph.　From the concentrate after removing the phthalic anhydride and the dibutyl phthalate content the surplus was namely the sample in tar.