The ecosystem for Hillside forest-rice, Named granaries, represents a typical geo-complexity in hilly regions of southern China. Cd’s accumulation in rice-fields mainly derives from industrial emissions - atmospheric depositions - hillside runoffs - hilly ponds - and rice fields. Hilly ponds are valued as a great agent for intercepting and retarding substances caused by cadmium’s migration, which is demonstrated in sedimental ways. We aim to clarify the sedimental mechanism of Hilly-ponds cadmium and offer a theoretical basis for cadmium’s interception in forest-rice systems, where water is utilized for irrigation. The research has been conducted by simulating hilly-ponds, where water had been collected from wild sites into lab-based models. To explore more details of deposition, researchers monitored cadmium in various forms which were affected by the dynamic changes of environmental factors, where exogenous hydrosphere had been excluded from the experiments to eliminate interferences of sustained inputs. The results can be concluded as:1. Mild acid-extracted form accounts for 91.5% of total sediment in Cd, while the remaining is in residual form.2. While cadmium is primarily colloid, both particulate and colloidal cadmium settle on the surface and middle layers of water as it transitions from Cd (aq.).3. Hydroxide ions (OH-) regulates cadmium’s transformation from Cd (aq.) into particulate and colloidal forms, yet, the supply of OH- is determined by metabolic activities of microalgae.Based on aforementioned conclusion, where microalgae exhibit strong activity and with high pH levels, Cd (aq.) can transform directly into particulate, before it settles to the bottom of water. Whereas in poor conditions of microalgae, along with decreasing pH value, Cd(aq.) transforms to be colloidal form and worsens, it retrogrades to Cd(aq.) with lower pH levels.Overall, Adding alkaline substances like lime or cultivating large aquatic plants can enhance pH levels in hilly-ponds, which accelerates cadmium deposition.