Transformation of Hg form in a soil-vegetable system during vegetable-growing period was studied by the methods of pot-culture experiment and sequential extraction-hydride atomic absorption spectrometry. Results showed that Hg in kale yard soil existed mainly in residue form and were influenced significantly by vegetable growth. The main changes of Hg form in kale yard soil were the significant decrease of water soluble and humic acids complexible Hg and the significant increase of organic substance-bound Hg. With increase of Hg introduced, the residue-bound and organic substance-bound Hg gradually transformed into exchangeable, carbonate-bound and Fe-Mn oxide-bound Hg, which resulted in the increase of Hg bioactivity and the decrease of vegetable biomass. Except organic substance-bound and residue-bound Hg, there were significant positive correlations between various Hg form, total Hg contents of kale yard soil and Hg contents in vegetable roots, stem and leaf.