<p>Ultrathin carbon foils have important applications in the field of space physics, particularly playing a key role in instruments such as space-based low-energy ion time-of-flight (TOF) mass spectrometers and neutral atom detectors. These particle detection devices utilize the charge exchange and secondary electron emission effects that occur when incident particles interact with ultrathin carbon foils. However, physical phenomena such as angular scattering and energy straggling that accompany these interactions can significantly impact key performance indicators of the instruments, such as resolution. To quantify these effects and optimize instrument design, this study employs the Monte Carlo particle simulation software Geant4 to model the energy loss characteristics of 2–50 keV hydrogen ions during their penetration through ultrathin carbon foils with nominal thicknesses of 0.5–2.0 µg/cm² (derived thickness:1.6–2.9 µg/cm²). Comparisons with prior experimental data demonstrate strong consistency in both the trend and magnitude of energy loss, aligning with the fitting laws of semi-empirical formulas derived from experimental measurements, thereby validating the simulation methodology. Furthermore, the investigation reveals the impact mechanism of material impurities on energy loss: Increasing (or decreasing) the proportion of impurity atoms identical to incident particles within the ultrathin carbon foil leads to corresponding enhancement (or reduction) in energy deposition. This systematic relationship establishes a crucial theoretical foundation for improving detector performance through material composition optimization.</p>