Germanium-antimony-tellurium (GST) alloys have emerged as dominant functional storage materials for phase change memory (PCM) due to their reversible crystalline-amorphous phase transition, outstanding thermal stability and reliable data retention capability. Driven by the booming development of the commercial satellite industry, PCM devices are confronted with severe reliability threats originating from space radiation environments. Specifically, the displacement damage effect induced by proton irradiation has been regarded as a critical factor deteriorating the storage performance and long-term service stability of phase-change materials. In this work, Geant4 Monte Carlo simulation was adopted to systematically explore the displacement damage effects of three typical GST alloys under proton irradiation in the energy range of 1~1000 MeV. Physical interactions including elastic and inelastic collisions between incident protons and target materials were numerically simulated, and key parameters of primary knock-on atoms (PKAs), the magnitude of non-ionizing energy loss (NIEL) and its in-depth distribution characteristics were quantitatively obtained. The simulation results demonstrate that 1 MeV protons yield the maximum NIEL, leading to non-negligible lattice displacement damage within GST materials. The nuclear reaction probability of incident protons increases monotonically with the elevation of proton energy. For protons with energies of 1~100 MeV, distinct Bragg peaks can be observed at the terminal range in NIEL depth distributions, and the peak positions gradually shift forward as proton energy increases. In contrast, protons with energies of 200~1000 MeV exhibit unremarkable Bragg features due to the reduced Coulomb scattering cross-section. In this energy interval, NIEL is primarily concentrated in the front range and declines with the increase of proton energy. Furthermore, the introduction of shielding layers can effectively modulate the NIEL deposition induced by low-energy protons in GST layers through the synergistic effects of shielding material species and layer thickness. At identical thicknesses, tungsten (W) shielding layers possess a superior NIEL mitigation capability compared to silicon dioxide (SiO2). Notably, a 6 μm-thick tungsten shielding layer can significantly suppress the proton-induced displacement damage in GST alloys.