Abstract: Calcium nano-montmorillonite(CaMMT)/ammonium polyphosphate(APP)compounds (CaMMT/APP) were prepared when different amounts of CaMMT were added at selected temperatures into the synthetic system of APP, and good dispersion of CaMMT and better thermal properties of the compounds were expected. The compunds were analysed by FTIR, XRD, TGA, ³¹P nuclear magnetic resonance (³¹P NMR), and their water solubility and pH were also measured. The completely exfoliated CaMMT is observed in the CaMMT/APP, indicating that CaMMT disperses well in APP. With the increasing content of CaMMT, the amount of APP with crystal form Ⅰ in the compunds increases, the degree of polymerization of APP decreases, and the initial degradation temperature of the compounds decreases, while the water solubilty of the compounds increases. However, higher contents of CaMMT help the compunds yield more residues at 800 ℃. With the same ammount of CaMMT, the higher the temperature, the more APP with crystal form Ⅱ with a higher degree of polymerization, and the water solubility of the compunds effectively decreases, and the thermostability of the compunds can be further enhanced. When CaMMT is added at 210℃, the relative mass of the residue of the compound is 29.69%, which is enhanced to 53.75% when CaMMT is added at 300 ℃.