重金属被土壤作物吸收后，通过食物链的传递和富集，最终危害人体健康。本文以西安市城北郊区蔬菜生产区为研究区，通过在典型样地设立隔离体，种植小白菜和茼蒿，在蔬菜生长期不同阶段同期采集土壤、蔬菜样品，测定样品中重金属Pb、Cd、Cr的含量，分析土壤-蔬菜系统中重金属的迁移转化规律。 结果表明，土壤中重金属Cd含量平均值为3.2mg/kg，超过国家土壤环境质量二级标准，重金属Pb和Cr含量的平均值分别是46.8 mg/kg、50.9 mg/kg，均未超标；小白菜中重金属Pb含量的最大值0.82mg/kg，超出无公害蔬菜的标准值约3.1倍，重金属Cd、Cr含量均未超标；茼蒿中重金属Pb的含量0.51mg/kg，超过无公害蔬菜的标准值约1.6倍，重金属Cd的含量0.08mg/kg ，超过无公害蔬菜的标准值0.6倍，只有重金属Cr的含量未超标。 土壤-小白菜系统中，重金属Pb、Cd、Cr的平均误差百分数分别是：1.47%、3.93%、3.34%，系统中三种重金属总量平衡。小白菜对于重金属Pb的吸收能力最强的是在其种植的14天后，小白菜中重金属Pb主要来自于20~30cm深度土层处；小白菜对于重金属Cd的吸收能力在其生长阶段变化不大；小白菜对于重金属Cr的吸收能力最强的是在收获前的7天，主要集中在20~30cm、40~50cm深度土层处。 土壤-茼蒿系统中，重金属Pb、Cd、Cr的平均误差百分数分别是：3.19%、3.55%、2.80%，系统中三种重金属总量平衡。茼蒿对于重金属Pb的吸收能力最强的是在其种植后的28天到收获前，茼蒿中的重金属Pb主要来自于0~10cm、20~30cm、40~50cm深度土层处；茼蒿对于重金属Cd的吸收能力最强的是在其种植后的28天到收获时，主要集中在0~30cm深度土层处；茼蒿对于重金属Cr的吸收能力最强的是在其种植后的23~28天，主要集中在30~50cm深度土层处。

Absorbed by soil-crop, heavy metal endangers human body health ultimately through the food chain transmission and enrichment. In research area which is in the north suburb production soil of vegetables of Xi’an, we set isolation body in typical samples and planted Tonghao and cabbage. In different stages of vegetables growing period , we collected soil and vegetable samples, measured the content of heavy metal including Pb、Cd、Cr, analyzed transform rule in migration of heavy metals in soil-vegetables system. The results showed that content of soil heavy metal Cd is in average for 3.2 mg/kg, more than the state soil environment quality secondary standard, content of heavy metal Pb and Cr for average 46.8 mg/kg、50.9 mg/kg respectively, failed to exceed standard; In Chinese cabbage, the maximum content of heavy metals Pb is 0.82 mg/kg which is beyond the standard value of non-pollution vegetables about 3.1 times, meantime, content of heavy metal Cd and Cr did not exceed standard; In Tonghao, the content of heavy metals Pb is 0.51 mg/kg, more than non-pollution vegetables standard value about 1.6 times, the content of heavy metal Cd is 0.08 mg/kg, more than pollution-free vegetables standard value 0.6 times, only the content of heavy metal Cr did not exceed standard value. In soil-Chinese Cabbage system, the average error percentage of the heavy metal Pb, Cd and Cr is: 1.47%, 3.93% and 3.34% respectively, so three kinds of heavy metals in system is balanceable totally. The most powerful absorption for heavy metals Pb of Chinese cabbage is after 14 days of its planted, heavy metal Pb in cabbage is major from 20~30cm depth of soil; The absorption of Chinese cabbage for heavy metal Cd in its growth stage is unchanged on the whole; Chinese cabbage, absorptive capacity for heavy metal Cr is strongest in the seven days before the harvest, mainly in 20~30cm, 40~50cm deep of soil. In soil-Tonghao system, the average error percentage of the heavy metal Pb, Cd and Cr is 3.19%, 3.55% and 2.80% respectively, so three kinds of heavy metals in system is balanceable totally. The strongest absorbing ability of Tonghao for heavy metal Pb is in its 28 days after planting and before its harvest. The heavy metal Pb in Tonghao is mainly from 0~10cm, 20~30cm, 40~50cm deep of soil; The strongest absorbing ability of Tonghao for heavy metal Cd is in 28 days after its growing to the harvest, mainly in 0~30cm depth of soil; The strongest absorbing ability of Tonghao for heavy metal Cr is after 23~28 days of its planting, mainly concentrated in the 30~50cm deep of soil.