The paraffin/diatomite form-stable phase change materials(PA/D-PCMs) was prepared by using solvent evaporation, diatomite as carrier and paraffin as phase change materials. The microstructure and thermal properties of PA/D-PCMs were characterized by SEM、FT-IR、DSC and TGA respectively. The results show that: Leakage of melting paraffin was hindered through both the hydrogen bonding and the capillary force of the pores of diatomite, hence PA/D-PCMs put up excellent thermal stability. At the same time, secondary pores of diatomite can restrict partial paraffin crystallization, crystallinity of which would be affected. In interior of diatomite there were a few conduction channels with intercommunication, which can enhance thermal conductivity of paraffin and accelerate paraffin heat storage and release. With increase of the paraffin content phonon scattering effect would become more fierce in X, Y and Z axis thermal conduction channel of PA/D-PCMs, so thermal conductivity of PA/D-PCMs diminish, but owning higher latent heat and crystallinity. In order to ensure PA/D-PCMs structure stable and have good thermal properties simultaneously, optimal paraffin fraction in the composite is 45%.