Abstract: The extraction equilibrium of uranium(Ⅵ) from phosphoric acid solution with HDEHP and TOPO in cyclohexane has been investigated to examine the effects of extractant concentration, hydrogen ion concentration and temperature on the extraction of uranium(Ⅵ). Experimental results suggest that the composition of synergistic complex species is UO2(HA2)2·/TOPO and the extraction equilibrium constant β21 is 109.52 at 30℃. In addition, the thermodynamic functions of the extraction reaction (△G,△H,△S) and the infra-red spectra of synergistic complexes have also been determined.