This article suggests a new method of determining the stability constant of ternary coordination complexes at liquid-solid interfaces in natural water, Its basic principle is based on the rule of left-right shift of an S-type curve, from which the "volcano" curve of exchange ratio E(%) vs concentration of organic matter is obtained. The volcano curve is further used to obtain the stability constant ratios(K-SAM/K-SM) by Using respectively the methods (1) of equality of E(%) at [H(2)A]=[H(2)A]o, and (2) of [H(2)A](max). From the known K-SM, the stability constant K-SAM of a liquid-solid interfacial ternary surface complex can be obtained.