Abstract: In this paper single and synergistic extraction by di-(1-methyl heptyl) methyl phosphonate(DMHMP)and 2-ethyl hexyl hydrogen 2-ethyl hexyl phos-phonic acid (HEHEHP) for thorium has been investigated respectively. There are three kinds of equilibria in the Th(No3)4-DMHMP-HEHEHP-C8C6 system:The equilibrium constants are determined by the usual slope method and found to be lgβ10=4.47, lgβ20=4.90, lgβ12 = 7.65 (20℃) .By determining the effects of temperature on the distribution ratio, △H , △Z and △S of reaction (2) and (3) are evaluated as follows; △H=-3.34 kcal· mol-1 , △Z=-6.57 kcal·moL-1, △S=-11.0 cal· mol-1·K-1 , for the second reaction. △S=-7.14 kcal ·mol-1 , △Z=-10.3 kcal·mol-1 , △S=-10.6 cal· mol-1·K-1, for the third reaction, In term of cone packing model a possible structure of the synergic extracting complex is proposed.