Abstract: The improvement of gaseous mercury concentration measurement technology is conducive to the accurate monitoring of atmospheric mercury, which can further provide technical support to the implementation of the “Minamata Convention on Mercury” and promote the prevention and control of mercury pollution in China. In this paper, a microwave digestion and inductively coupled plasma mass spectrometry (ICP-MS) was developed to measure the concentration of gaseous mercury. Specifically, the factors affecting the experimental results were evaluated, including (1) the factors of activated carbon particle size and gas flow to mercury adsorption in sample preparation, and (2) the factors of digestion temperature, volume ratio of HNO₃∶HCl and digestion time to the digestion efficiency in sample pretreatment. The external standard method for the quantitative determination of mercury based on ICP-MS was also established. The results showed that 50 mesh activated carbon and lower gas flow were more favorable for the adsorption of gaseous mercury, and the best efficient digestion was obtained when the digestion temperature was 190℃, the volume ratio of HNO₃∶HCl was 5∶3, and the digestion time was 50 min. In this method, the linear correlation coefficient R² is 0.9999 and the detection limit is 0.0509 ng·g⁻¹, which shows good linearity and a lower detection limit for the measurement of gaseous elemental mercury. The samples were determined by the external standard method based on the certified reference material of single elemental mercury. The differences between the results calculated by the external standard method and the theoretical data are less than 2.5%, which proves the high accuracy of this method and further verifies the accuracy of the quantity of mercury gas standard prepared by the dynamical generation method.