Abstract: Syntactic foam with volume fraction of 65% —70% synthesized by vacuum assisted molded forming of hollow glass microspheres (HGMs) named HGS8000 X in epoxy resin matrix is characterized for the effect of volume fraction of HGMs on density, the compressive strength, moisture absorption properties and resistance to hydrostatic pressure of syntactic foam in the present study.The results shows that moisture absorption is less than 1% after hydrostatic test of 50 MPa, 24 h, and the density can reduce to 0.60 g/cm³ from 0.65 g/cm³ under the compressive strength greater than 80 MPa, namely, syntactic foam has the best overall performance, while volume fraction of HGMs is 67% —69%.The study provides an insight into the performance of high microspheres levels of syntactic foam depends on a greater degree of the changes in the material microstructure caused by the lack of epoxy resin and the stress state of HGMs.