Abstract: A Two-phase Titration Method has been used tor the investigation of solvent extraction mechanism of Ni⁺⁺、 Co⁺⁺and Cu⁺⁺with Di-2-ethylhexyl-phosphoric acid. The method is very simple and rapid. In the experiment we only want to determine the variation of pH, and calculate the extraction constant. In the ranee of concentration studied, metal ion (Mi⁺⁺、 Co⁺⁺ and Cu⁺⁺) is extracted into the organic phase by HDEHP-C₆ H₆ system with the formation of MA₂·2HA.