A novel epoxy resin (EP)/hollow glass microsphere modified (g-HGM) composite was successfully prepared. Studies showed that the water absorption rate of the g-HGMs/EP composite is lower than pure HGMs/EP and HGMs-KH550/EP composites, while the compressive strength of g-HGMs/EP composites could be increased. The enhanced interfacial adhesion between EP and g-HGMs played an important role to improve the compatibility of the two components. The g-HGMs show little effect on density (relative to HGMs) on the g-HGMs/EP composites, which can perform better than the HGMs/EP composites being used in marine environments. It was found that the optimal content of 4,4’-diphenylmethane diisocyanate in the epoxy component was 20 wt%.