Abstract: Glass fiber reinforced plastic (GF/EP) serves as an ideal support material for beam pipes in applications such as BEPC II and CEPC. However, its compressive strength is prone to degradation in irradiation environments, impacting the operational reliability of supporting equipment. To enhance its compressive strength under γ-irradiation, organic montmorillonite (OMMT) was chosen as the modifier in this study to form OMMT-GF/EP composite by hot-pressing process and the evolution of compressive strength under different γ-irradiation doses was systematically investigated. The interfacial strengthening mechanism was further analyzed by SEM, XRD, FTIR, and XPS. The results reveal that the incorporation of an appropriate amount of OMMT effectively enhances the compressive strength of GF/EP under γ-irradiation, with the 3wt%OMMT-GF/EP exhibiting the optimal performance. After irradiation doses of 20 kGy, 200 kGy, 1000 kGy, and 2000 kGy, the compressive strength elevates from 267.87 MPa to 292.24 MPa, 297.79 MPa, 317.05 MPa, and 319.82 MPa respectively, with the highest increase rate of 19.39%. SEM analysis reveals that OMMT enhances the bonding between the resin matrix and glass fibers during irradiation. XRD results reveal that OMMT is generally well dispersed in the epoxy matrix, although a certain aggregation tendency appears at high loading levels. The result of FTIR and XPS indicate the formation of Si—O—C between OMMT and the resin under γ irradiation, thereby enhancing the compressive strength of OMMT-GF/EP composites. These results demonstrate that the γ-irradiation-induced interfacial strengthening effect is the primary mechanism responsible for the enhancement of compressive performance in OMMT-GF/EP composites, providing valuable guidance for the design and fabrication of radiation-resistant GF/EP materials.