Abstract: Based on the pseudobinary method and solute aggregation model of aqueous solution, a pseudobinary solute aggregation model for correlating the viscosity of water-organic solvent-salt solution is established. The model has been tested for ternary aqueous solutions saturated or unsaturated with salt. The average relative deviation is about 1.0%. The results are better than the pseudobinary local composition model presented early by authors. The model parameters vary regularly with the concentration of salt and temperature for unsaturated solution.