Abstract: The relationship between NaCl concentration and light intensity of burning NaCl aerosol in the range of 4 ng/m³-13 mg/m³ during the sodium flame efficiency test of HEPA filter was studied, the experimental data were analyzed by the least square method. The result shows that there is a linear relationship between photo current and NaCl concentration in the range of low concentration, and the self adsorption coefficient of NaCl light spectrum is 1. However, there is no linear relationship in the range of middle and high NaCl concentrations while the higher the concentration, the less the linear relation, and the smaller the self adsorption coefficient. In a word, for HEPA filter test, the efficiency calculation equation of the national standard can be used when the NaCl concentration is lower than 0.05 mg/m³, or the new relation curve should be adopted through calibrating the photo current of sodium flame photometer for different NaCl concentrations.