Effects of edge-sealing on water absorption of glass fiber reinforced epoxy resin composites (GF/E-51) were investigated by weight measurement and volume measurement of composites specimen. The experimental results show that the diffusivity coefficient of edge absorption is far more than that of the surface absorption and the maximum moisture content of the unsealed specimen increases by 73.8%. Meanwhile, the volume dilatation of the unsealed specimen increases by 200.1%, which indicates that the mechanism of water absorption of GF/E-51 can be classified into two types: open-porous absorption and close-porous absorption. Water behaves as a vapor-phase in the porous close composite, but as a liquid-phase in porous open absorption.