Abstract: The effects of design parameters such as the scintillation crystal materials, the thickness of borehole shield and the surface density of boron sleeve on the logging response of the formation element logging tool were studied by using Monte Carlo method. The results show that LaBr₃ detector has outstanding performance in logging response compared with BGO detector. Salt water with high salinity affects ultimately the measurement of the element concentrations. The borehole shield thickness of 1.2 cm can shield more than 60% γ-ray from borehole. ¹⁰B surface density of 0.065 g/cm² can eliminate the capture γ background from tool material. With the increase of formation porosity, the investigation depth of capture spectrum decreases. The investigation depth of inelastic spectrum is about 14 cm, which is almost identical among the formations with different porosities.