Rsversed phase paper chromatography has been used to study the mechanism of extraction of the ions of rare earths, uranium (}'I)，copper, calcium and zinc by hydrogen di (3-ethylhexyl) phosphate(HDEHP).When a suitable non-volatile solvent is introduced to the paper, the oxperi-mental results show great similarity between the extraction mechanism of HDEHP inliquid-liquid extraction and the chromatographic behation of paper treated with HDFHP.The results obtained in this paper are in contrary to the conception of Cerria who assumed that there existed two kinds of retention mechanisms in extraction chromatography.