A composite hydrogel with interpenetrating network structure was prepared via in-situ synthesis of calcium phosphates during the physical-chemical crosslinking of poly (vinyl alcohol) (PVA) and poly (acrylic acid) (PAA). The hydrogel water content was tested. Fourier transform infrared absorption spectrum (FT-IR), X-ray diffraction and scanning electron microscopy were employed to evaluate the characteristics of the composite hydrogel. The results showed that the composite hydrogel had high water content and that the inorganic phase was poorly crystalline calcium phosphates. FT-IR confirmed that the interpenetrating network structure was formed between PVA and PAA. The chemical interactions between inorganic and organic phases were further investigated and discussed. The composite hydrogel with an interpenetrating network achieved using the present novel method could be a promising material for tissue engineering.