The study on the chemical fractionation and bioavailability of heavy metals from non-contaminated and sewage-irrigated soils of Sizhuangding in Xinxiang showed that,total Cd,Ni,Zn,Cu and Cr concentrations of non-contaminated soils achieved the national standard for soils,and sewage-irrigated soil Cr concentration achieved the national standard for soil,while Cd,Zn,Ni and Cu concentrations were over the standard,with the average contents being 65.31,1196.64,2799.25,145.78 mg/kg.The average concentrations of Cd,Zn,Ni and Cu were 65.31,19.94,9.33,1.46 times of national standard for soil,respectively.Sequential extraction rusults showed that,Cd was dominated by iron-manganese oxides fraction,with the percentages being 56.84%.Ni was dominated by iron-manganese oxides fraction and residual bound fraction,with the percentage being 37.44% and 39.55%.Zn was dominated by residual bound fraction,with the percentage being 78.24%.Cu was dominated by organic fraction,with the percentages being 57.70%.Cr was dominated by organic fraction and residual bound fraction,with the percentages being 45.50% and 34.18%.Compared with the non-contaminated irrigation soils,percentage of Cd,Ni,Zn,Cu,Cr residual fractions in the contaminated soils reduced,which could increase the heavy metal mobility and bioavailability.For exchangeable fraction and bioavailability of Cd being higher than Zn,Ni,Cu with the percentages being 24.54%,we should pay attention to the mobility and phyto-toxicity of Cd.