Abstract: This study focuses on investigating the damage mechanism of 3 MeV proton irradiation on the electrical properties of diamond Schottky barrier diode (SBD), with the core purpose of providing critical theoretical support for the radiation hardening of diamond-based electronic devices deployed in harsh space radiation environments. And as diamond emerges as a promising wide-bandgap semiconductor for high-power, high-temperature, and radiation-resistant applications, understanding how proton irradiation degrades its device performance is essential for advancing its reliable use in space missions and other radiation-exposed scenarios. To achieve this objective, a comprehensive experimental and simulation approach was adopted. The pristine diamond SBD was subjected to systematic electrical characterization using four key techniques—current-voltage (I-V) measurement, capacitance-voltage (C-V) measurement, low-frequency noise (LFN) spectroscopy, and conductance/angular frequency (G_p/ω) analysis—then the devices were irradiated with 3 MeV protons under controlled experimental conditions, and the same set of electrical characterization methods was repeated to capture post-irradiation changes, while complementary numerical simulations were performed using stopping and range of ions in matter (SRIM) software to predict the distribution and density of proton-induced bulk defects in the diamond material, and technology computer-aided design (TCAD) tools were employed to model the impact of these defects on the device’s electrical behavior. The combined experimental results demonstrate that 3 MeV proton irradiation introduces abundant defects in diamond SBD, which act as effective carrier recombination centers and significantly alter the device’s electrical properties. From the I-V characteristics, the forward current density decreases substantially from 0.41 A·cm⁻² to 0.21 A·cm⁻², while the Schottky barrier height increases from 1.11 eV to 1.23 eV and the ideality factor rises from 1.84 to 1.96. The C-V measurement results further confirm a reduction in the drift region carrier concentration from 6.97×10¹⁵ cm⁻³ to 5.86×10¹⁵ cm⁻³ post-irradiation, accompanied by a notable expansion of the depletion region width from 215.92 nm to 346.83 nm. The LFN spectroscopy results reveal a marked increase in the device’s defect concentration after irradiation, which directly leads to a higher current noise spectral density. And for interface state defects specifically, the G_p/ω analysis shows a significant post-irradiation increase in their concentration, with the corresponding trap energy levels shifting toward deeper positions within the diamond bandgap. The SRIM and TCAD simulation results show, confirming that the increase in donor bulk defect concentration exacerbates the degradation of device performance, and collectively, both experimental and simulation findings illustrate that the deterioration of diamond SBD electrical properties after 3 MeV proton irradiation arises from the synergistic effect of increased interface state defects and modified donor bulk defect concentration. Thus, this study not only clarifies the fundamental damage mechanism of proton irradiation on diamond SBD but also offers an important theoretical reference for optimizing the radiation resistance of such devices.