The invention discloses a method for purifying phosphoric acid, and the method comprises the following steps: no-load solvent and phosphoric acid are added to an extractor, and the loaded solvent from the extractor that contains P2O5 enters a fine desulfurization groove in light phase after phase separation; then BaCO3 solution which is dissolved by washing acid is added to the fine desulfurization groove; the load solvent after fine desulfurization is sent into a washer by a pump; in the washer, the load solvent is washed by the washing acid which is the product acid obtained after back extraction; 30 t0 70 percent of the washing acid returns to the fine desulfurization groove directly and pre-washes the loaded solvent, and the residual washing acid is used for dissolving BaCO3; the loaded solvent after washing enters a back extractor and back extraction is executed with desalted water; and phase is separated under gravity function, the lower layer of the liquid phase is the product, and the solvent returns to the extractor to be reused. The method has simple process, is easy to operate and control and is suitable for industrialized production.