The invention discloses a synthesis method of citric acid phosphoric acid ester, which is characterized by comprising the following steps of stirring citric acid with benzoic alcohol to react at 145 DEG C-190 DEG C for 5-12 hours, distilling unreacted benzoic alcohol by pressure reduction at 175 DEG C-185 DEG C after reaction, and re-crystallizing by anhydrous alcohol; under the protection of N2, dissolving the products in benzene or cyclohexane solvent, placing mixture into an ice-bath at 3 DEG C-5 DEGC, slowly dripping benzene solution dissolved with PC15 into the solution, keeping the reaction temperature at 2 DEG C-8 DEG C, dripping for 1-4.5 hours, continuously stirring to react for 0.5-1 hour, slowly adding water to the solution, keeping the temperature constant, stirring for to react for 0.5 h after white solid is separated out, carrying out suction filtration and drying; and catalyzing above products by 10%Pd/C with weight ratio of 2-5% at normal temperature and pressure in the distilled water for 5-10 hours, carrying out suction filtration, washing by the distilled water, and adjusting the pH value to be 7. The invention has the advantages of cheap raw materials, gentle reaction conditions and high yield.