Using 234Th, 228Ac and 139Ce 3 for tracer and HDEHP as an extractant, an effect of concentration of HNO3 solution on the extraction efficiency of 234Th, 228Ac and 39Ce 3 has been studied. It has been found that 234Th can be extracted quantitatively from HNO3 solution by HDEHP within extensive concentration of HNO3 solution. When the HNO3 concentration is higher than 2.0 mol/L, the extraction efficiency of 228Ac and 39Ce 3 is lower than 2.0%. The relation between shaking time and the extraction efficiency of 234Th was investigated. Experimental data shows that the extraction equilibrium can arrive within 1 min. The experimental result that the traces of actinium were separated from large amount of thorium, indicates that the separation of actinium from thorium is possible and loss of actinium is little.