A study on chemical reactions concerning adsorption, oxidation-reduction and complexation of low-molecular weight organic reducing substances with soil was carried out. Results show as follows: About 60%~75% of the total organic reducing substances added was adsorbed by the soil, consisting roughly by half and half of strongly and weakly reducing organic substances. The adsorption of negatively charged substances varied with the content of Fe/Mn oxides and the negative charge they bear in the form of electrostatic adsorption. The adsorption of –COOH/-C^=O _-NH2 containing functional groups demonstrated existence of complexation on the solid surface; In redox equilibrium organic reducing substances acted as electron donor reducing Fe₂O₃ and MnO₂ and got oxidated themselves; The complexation process was controlled by chelation-dissociation equilibrium in the solution and strongly affected by the amount of ligands and the amount of complex radicals that compete for ligands with hydrogen ions.