This basic study investigates the ratio of peak to total (ܴ) and peak to source ‫)ݏߟ(‬ for Si-PIN detectors in X-ray fluorescence (XRF) analysis, with emphasis on analysis the parameters for ܴ and ‫ݏߟ‬ using the Monte Carlo method. Many XRF system models have been simulated using the Monte Carlo Neutron-Particle Transport Code MCNP5. Various parameters are set to calculate the detection efficiency in those models, such as the desired X-ray collection angle, thickness, density, moisture content, X-ray angles, geometric distance, and so on. These parameters can impact ܴ and ‫ݏߟ‬ in the exponential form to some extent. This study provides a convenient and reliable method for the passive calibration of XRF measurements.