The humic substances including humic acid (HA) and fulvic acids (FAs) extracted from a refuse compost were investigated the average conditional concentration quotients of the complexes formed by the reaction of heavy metals with the humic substances. The characteristics of these humic substances were previously investigated by a related study. The concentrations of the free ions of Pb, Cu, Cd, and Zn in the reaction systems of heavy metal-HA suspensions and heavy metal-fulvic acid (FA) solutions were measured by anodic stripping voltammetry (ASV). The sequence of the average conditional concentration quotients of the complexes formed from the reaction of humic substances with heavy metals was FA (MW<1000) > FA (MW>1000) > HA (MW>1000). The sequence of reacting heavy metals with humic substances was Pb > Cu > Cd > Zn. Reactions of refuse compost-derived humic substances with heavy metals thus affect the mobility and biotoxicities of heavy metals in soil and the associated environments.