A thermodynamic model based on chemical equilibria with mass and charge balance equations has been developed for the solvent extraction system consisting of ZnSO₄–H₂SO₄–H₂O-D2EHPA-kerosene. The activity coefficients of all solutes in the aqueous phase were calculated by Pitzer’s equation. By applying this model, the equilibrium concentrations of solutes were calculated from the concentration of zinc and pH . The extracted metal species was ZnHA₃ and extraction equilibrium constant was found to have a value of 9.77×10⁻² from the slope of the equilibrium extraction data. The predicted distribution coefficients of zinc were in good agreement with experimental results.