Space charge accumulation causes the local electric field distortion, resulting in insulation breakdown. In this paper, space charge characteristics of boron nitride (BN)/epoxy nanocomposite dielectrics modified by iron oxide fillers are studied under DC electric field. Firstly, the boron nitride nanosheets and nano-magnetic γ-Fe2O3 epoxy nanocomposites were prepared. Then, the space charge characteristics and electric field distribution of nanocomposites were measured by PEA method. It indicates that 0.5 wt% BN nanoparticles can achieve the excellent space charge suppression effect, while 0.1 wt% modified BN nanoparticles present favourable uniform electric field distribution. It can be concluded that the BN nanoparticles modified by γ-Fe2O3 can improve the space charge accumulation in epoxy insulation. Reduction of interface charge accumulation contributes to the space charge improvement. It provides a guide for insulation optimization of power electronic equipment.