The metobolism of K, Ca, Mg and microelement in the root of Phaseolus raditus L. were studied. By flame atomic absorption spectromentry (FAAS), the concentration of K, Ca, Mg, Zn, Cu, Fe and Mn in the root of mung bean seedlings at the initial stage of growth under cadmium stress (1 mu mol/L) were determined. It shows that the concentration of K, Mg and Mn in the root are decreased, but Ca, Zn, Cu, and Fe are increased. So, it indicated that Cd did harm, indirectly, to the root of mung bean seedlings at the initial stage of growth.