Abstract: This paper studied the synergistic extraction of Uranium (Ⅵ) from sodium perchlorate solution with ternary system of 1-phenyl-3-methyl-4-caprylyl pyrazolone-5 (PMCP or HA),thenoyl trifluo-roacetone (TTA or HT) and diisoamyl methyl phosphonate (DAMP or B). The formation of a singlet extracted complex UO2A2,two binary adduct complexes,i, e. UO2A2B,UO2T2B and a ternary extracted complex UO2ATB were confirmed by slope analysis. The equilibrium constants at 25±1℃ were determined to be KA = 10-0.42(UO22+ + PMCP system) , KAB = 104.21(UO22+ + PMCP + DAMP system) and KATB = 104.27(UO22+ + PMCP + TTA + DAMP system) respectively.The mechanism of extraction and structures of the extracted species have been discussed.