Abstract: Method of continuous countercurrent extraction was used to purify raw material phosphoric acid by wet process at first.Then ammonia was used to directly back extract the organic solvent after extraction to produce ammonium phosphate crystals.Finally the crystals were separated from the organic extraction agent by deposition to achieve the aim of recycling utilization of organic extraction agent and direct crystallization of ammonium phosphate through back extraction.Experiment results showed that the optimum technological conditions of producing ammonium phosphate with the method of solid-liquid back extraction of wet process phosphoric acid were as follows：extractants′ composition was V(tributyl phosphate)∶V(diluent)=1∶1，mass fraction of P₂O₅ in raw material phosphoric acid was at 40%~50%，volume ratio of extractants to phosphoric acid was about 3∶1，extraction stirring time was about 5 min，ammonia amount was that control pH≈7 of the liquid phase after backextracted crystallization,and stripping-crystallization temperature was 15~20 ℃.Ultimately in the obtained ammonium phosphate crystalsw(N)>20%andw(P₂O₅)>50%，and one time utilization ratio of P₂O₅ in the phosphoric acid by wet process approached 50%.Contents of N and P in ammonium phosphate crystals made by this method were both close to the industrial DAP (98%) standard and were much higher than national fertilizer grade ammonium phosphate product standard.

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