Hydrothermal method was used to prepare the hydroxyapatite (HA) coating on CaO-SiO2-B2O3-Na2O glass. The phase composition, morphology and microstructure of HA coated glass composites were analyzed using XRD, EPMA, FT-IR and SEM techniques. It revealed that HA coating possessed a porous gradient construction; HA coating was tightly bonded with the glass substrate by the interface layer. During the formation of HA coating, the hydrated silica produced by the corrosion of glass substrate in the hydrothermal solution provided favorable sites for apatite nucleation. With the dissolving of HA powder and the growth of apatite small crystallites, Ca+, PO(4 (3-)) ions would precipitate on the surface of glass to form the HA coating. Silicon element released from glass reacted with calcium produced by the dissolution of HA to form the tight reaction layer. HA coating is formed by the mechanism of dissolving-ions immigrating-precipitating pattern.