In order to meet the requirement of radiation shielding materials for space nuclear reactors, gamma shielding effect of epoxy resin base added with Gd 2 O 3 /Bi 2 O 3 particles was studied by Monte Carlo simulation platform Geant4 in this paper. Firstly, the gamma ray shielding effects of functional ller with different ratios and content were simulated. Then, based on the gamma-ray energy range generated by space nuclear reactors, the γ-ray protection performance of epoxy resin composites under different energy ranges was studied. Finally, the effects of the particle size and arrangement of the llers on the γray shielding properties of the composites were presented, and the results showed that the smaller of the particle size, the better the shielding effect will be; for the same size of the ller, the arrangement of the ller with a larger projection area has a better γ-ray shielding performance. The effect of Gd 2 O 3 /Bi 2 O 3 added to epoxy resin base on low-energy gamma rays is obvious, but the effect on high-energy rays is less.