Abstract: In the purified phosphoric acid,the content of impurities is very low except fluorine.In order to obtain food grade and purer phosphoric acid,it′s necessary to search appropriate methods for deep defluorination and get their rules.The effects and rules of defluorination were studied with the methods of vacuum evaporation,vapor stripping,and crystallization,and condensed purified phophoric acid was repeatedly recrystallized by solution crystallization.The experiments results showed that vapor stripping and crystalliztion methods are more appropriate for deep defluorination than vacuum evaporation method;the fluorine mass concentration in condensed phosphoric acid can be decreased to lower than 10 mg/L from  70 mg/L to meet food grade phosphoric acid standard by vapor stripping for 1.5 h under the vacuum condition of  0.065-0.07 MPa, and the same result could also be reached by one time of solution crystallization;In the crystallization process,the distribution ratios (D) of defluorination increased with the decrease of fluorine content  (Y)  in crystallized mother liquor,and their relations can be expressed by equation D＝0.774 1Y -0.493 3 if the mass concentration of fluorine in raw phosphoric acid is below 120 mg/L.