Abstract: Objective The added value of cesium nitrate, as the ionization inhibitor, on the ionization of potassium and sodium solution by flame atomic absorption spectrophotometry was discussed. Based on method described by the GB 11904-89 "the Determination of Potassium and Sodium in Water by Flame Atomic Absorption Spectroscopic", the addition of cesium nitrate in determination of airborne toxic substances in workplaces was revised. Methods Under the optimized condition of testing instrument, the standard curve,detection limit, precision and accuracy were tested, and the inhibition results were statistically analyzed. Results The optimized concentrations of cesium ion were 341 mg/L and 682 mg/L respectively for the determination of sodium and potassium. After addition of cesium nitrate, the correlation coefficient of sodium curve was 0.999 6, the linear range was 0.0-5.0μg/mL, the detection limit was 0.007μg/mL and the lowest detection concentration was 0.001 mg/m³. For Potassium, the correlation coefficient was 0.999 4, the linear range was 0.0-10.0μg/mL, the detection limit was 0.015μg/mL and the lowest detection concentration was 0.002 mg/m³. Conclusion The optimized value of cesium nitrate as the ionization inhibitor could improve the sensitivity.