Abstract: The relationship between morphology and occurrence conditions of heavy metals is key to assessing the risk of heavy metals in soil. In this paper, the authors studied Pb and Cd soil related to gold mining, analyzed the impact of such factors as organic matter, clay, pH and Eh in soil on bioavailability by means of the kinetic equation. The results show that the main factors affecting bioavailability are soil organic matter, pH and Eh. The content of organic matter has a distinct relationship with Pb or Cd in soil．Also, the increase in clay content in soil may slightly increase the proportion of the content of Cd and Pb in the ionic exchangeable form to the total content of Pb and Cd. The soil acidification may increase the content of cadmium in the ionic exchangeable form, which has a distinct relationship with the pH in soil. Bioavailability is weakened with decreasing soil Eh. It is obvious that the increase in organic matter in soil may obviously reduce the content of Cd and Pb in the ionic and exchangeable form. When the effective state is considered, the maintenance of soil weak acidification or weak alkalinity is a good way to avoid active bioavailability. When the crops mature, the implementation of flood irrigation can inhibit the accumulation of heavy metals in grain.