Abstract: Isotope dilution-α spectrometry for separation and determination of 239,240Pu in soil is developed. With Pu isotope dilution method, tetravalent plutonium is extracted from 7.5 mol/L nitric acid into TOPO/toluene. After plutonium is back-extracted with 0.01 mol/L oxalic acid, α source is prepared with aqueous phase. α counting rate of Pu isotoped is measured by the low background α spectrometry. After data processing, the concentration of 239,240Pu is achieved.