Abstract: An equation regarding molecular species distributions of the mcthylolderivativcs of polyamine compounds has been derived by the probability method in terms of one-shell substitution effects.The relationship between probabilities of generating various methylolderivatives and kinetic paramenters describing the substitution effects in initial stage and in equilibrium state of the amino-formaldehyde reaction has been obtained.The results based on the theoretical equations are good in agreement with experimental data.