Apparent equilibrium constant βa and complex formation constant n of PVA with Zn2+ and Cd2+, and of chitosan(CTS) with Zn2+ were determined.The initial concentrations of metallic ion and polymer ligand were changed and the concentration of the residual metallic ion was determined.The data were put in an equation to form a series of relationship formulas between n and lgβa.The curve drawing software Origin was used to plot the resulting curves to give a set of crossing points.