Abstract: NO₃^- and Mo₇O₂₄^6- intercalated ZnMgAl ternary layered double hydroxide (NO₃-ZnMgAl LDHs, Mo-ZnMgAl LDHs) was prepared by the hydrothermal method and ion exchange, respectively. The flame retardancy and smoke suppression of polyurethane elastomer (PUE) composites were studied by adding two ternary LDHs with different proportions. Both the cone calorimeter combustion and smoke density tests show that the peak heat release rate (PHRR) and maximum smoke density (D_{s, max}) of the pure PUE are 920 kW/m² and 452, respectively. When the mass fraction of NO₃-ZnMgAl LDHs is up to 7wt%, the PHRR and D_{s, max} are 377 kW/m² and 216, respectively. With the same loading of Mo-ZnMgAl LDHs, the PHRR and D_{s, max} are 343 kW/m² and 190, respectively. Both ternary LDHs possess notable flame retardancy and smoke suppression effects on PUE composites. LDHs/PUE composites have better flame retardancy and smoke suppression with Mo-ZnMgAl LDHs. TGA measurement confirms that the addition of two ternary LDHs can both promote the charring formation of LDHs/PUE composites and improve the char residue rate. LRS and XPS confirm that they could improve the graphitization degree of the char residue which can in turn enhance the thermal oxidation resistance of the char layer. Furthermore, the Mo-ZnMgAl LDHs can raise the char residue and graphitization degree and strengthen the thermal oxidation resistance, which could effectively protect the substrate material from heat radiation, and consequently oxygen could be isolated, meanwhile, the volatilization of combustible gas could be restrained.