The solubility of NaHCO3 was determined in the NH4+-Na+-CO32--HCO3--Cl--H2O system with the concentration up to 6 mol.kg(-1) by a dynamic method from 283.15 to 333.15 K. It was found that the solubility of NaHCO3 decreases with increasing concentration of Na2CO3, NH4HCO3, or NaCl. A speciation-based model was developed with mixed-solvent electrolyte interaction parameters newly obtained by regressing both the experimental and literature solubility data. The average relative deviations are less than 5.0%. The new model is able to predict the solubility of NaHCO3 at high pressures up to 6.0 MPa for the NH3-CO2-NaCl-H2O system at 313.15 and 323.15 K. This work can provide a theoretical basis for producing Na2CO3 with a better crystal form and higher productivity in the carbonation process.