This work intends to model the equilibrium swelling behavior of highly branched polyamines. The developed model consists of three components: ionic, elastic and mixing. In this model, the ionic swelling pressure is explained using Donnan equilibrium swelling, Flory-Rehner phantom and affine network expression is taken into account for elastic components, and finally Gibbs energy of mixing is used for mixing contributions. Molar fraction of effective charges, named f parameter, is used in the gel swelling. The obtained results indicate that the volume swelling ratios of hydrogels in water are increased sharply by repeating mole fraction of poly(amidoamine). Comparing our theoretical results with the calculated results of Unal and Hedden, and also their experimental data, the validity of the proposed model is revealed. In comparison with the model proposed by Unal and Hedden, errors are decreased by 65.56%.