In geochemical elemental logging, the elemental sensitivity factor is a key parameter for converting relative yields of elements obtained from spectral analysis to actual concentrations of the elements in the formation. Here we perform a quantitative analysis of the Monte Carlo N-particle (MCNP) simulated spectra of elements in a model formation and compare the obtained relative yield of each element with its actual dry weight in a model formation to study their relationship. For a series of model formations with simple and complex lithologies, the mixed formation spectrum was obtained through MCNP simulation, and elemental sensitivity factors in these formations were calculated according to elemental sensitivity factor theory and applied in calculating dry weights of actual formation elements. It is thus inferred that the elemental sensitivity factor is a constant quantity and does not vary with the nature of the formation. The elemental sensitivity factors calculated for the simulated formations are close to actually measured sensitivity factors and can be used to analyse actual formation elements.