The competitive adsorption of Zn,Ni and Co from 10^-4-10⁺⁶ molLu^-1 heavy metal ions solution containing 0.05mo1L^-1 Ca(NO₃)₂ (pH5.5) by three soils with different pl:ystcai and chemical properties was investigated.The results obtained showed that the amount of heavy metals adsorbed by soils was in the sequence: Yellow brown earth>Latosol>Red earth.The order of ion selectivity was: Zn>Ni≥Co.Obviously,the mechnism of competitive adsorption differed from that of non-competitive adsorption.Firstly,the quantity of competitive adsorption exceeded that of non-competitive adsorption.Most of all,the heavy metal ions,especially Zinc,adsorbed by the samples in which free iron oxide was removed increased to varying degrees instead of decreasing.Obviously,the effect of accompanying anion on the quantities of heavy metals adsorbed was greatly inhibited.The change of pH₅₀ which could reflect the interaction between soil and heavy metal ionsw Leas in consistent with the characteristics of adsorption isothirm.Secondly,according to the characteristics of adsorption and desorption of heavy metal ions,it might be considered that the adsorption sites on colloid surface in red earth were less than those in yellow brown earth and latosol,but red earth had a higher proportion of high energy adsorption sites than yellow brown earth and latosol.