The invention discloses a synthesis method of solifenacin succinate. The synthesis method comprises the following processing steps: (1) respectively dissolving (S)-1-phenyl-1,2,3,4-tetrahydroisoquinoline, organic alkali and triphosgene into a proper amount of high-boiling-point solvent, dropwise adding the (S)-1-phenyl-1,2,3,4-tetrahydroisoquinoline and a solution of the organic alkali to the solution of the triphosgene, so as to obtain an intermediate (S)-1-phenyl-3,4-dihydro-1H-isoquinoline-2-formyl chloride, and finally adding a proper amount of organic alkali and high-boiling-point solvent, adding (R)-3-quinuclidinol, heating to 100-200 DEG C and carrying out temperature control reaction, so as to prepare solifenacin; and (2) dissolving the solifenacin into a mixed solvent of ethyl acetate and ethyl alcohol, adding new seed crystal of the solifenacin succinate, stirring and crystallizing, so as to prepare the solifenacin succinate. The synthesis method of the solifenacin succinate has the advantages that two-step condensation reaction is carried out by virtue of a one-pot operation in the synthesis method, so that the troublesome azeotropic separation operation reported in the literature is avoided; and homogeneous catalysis is carried out by selecting soluble organic alkali, so that the reaction efficiency is improved.