In this paper, nylon was used as carbonisation agent instead of pentaerythritol (PT), and the melt intercalation method was used to synthesise polypropylene (PP)/nylon (PA6)/montmorillonite (MMT) flame retardant nanocomposites. The structure and flammability property of products were characterised by X-ray diffraction, Fourier transform infrared spectroscopy, transmission electron microscopy, thermogravimetric analysis (TGA), cone calorimeter test, limiting oxygen index and vertical burning test. The results showed that the polymer chain was intercalated into the MMT's interlayer and the MMT dispersed into PP/PA6 matrix in the form of intercalation to get flaky texture. The appropriate content of MMT in composition is 4-6 mass%. The use of intercalated MMT increased the tensile strength of materials by 15.0% and the impact strength by 69.5%, and improved the flame retardant properties. The TGA showed that the char residue rate reached 12.3%. The cone calorimeter experiments indicated that the peak of heat release rate reduced by about 87% in comparison with the pure PP and the residue weight increased. The vertical burning test (UL 94) results indicated that the materials achieved V-0 grade.