Abstract: ZnMgAl layered double hydroxides(LDHs), modified-LDHs and Sb₂O₃-LDHs were prepared via rapid nucleation/crystallization method, and modification by sodium oleate and high-speed ball-milling process, respectively, and then were characterized by XRD, FTIR, FESEM and TG etc. The flame retardant and mechanical properties of soft polyvinyl chloride(PVC) matrix composites with 6% mass ratio of Sb₂O₃-LDHs were investigated. The results show that all the composites can meet the requirement of V-0 grade in UL-94 test and the LOI value reach to 33.4%; the mechanical properties of modified-LDHs/soft PVC and Sb₂O₃-LDHs/soft PVC composites can be improved in certain extent. The FESEM images of the carbon residue after combustion show that a dense protective coal layer forms on the surface of composites after combustion to achieve flame retardant effect when adding modified-LDHs or (Sb₂O₃)₁₀-LDHs. FESEM images of materials' cross-section show that the modified-LDHs is dispersed uniformly in the soft PVC, and exhibit well compatibility with soft PVC, enabling strengthen and toughen the composites. The elongation at break and tensile strength of Sb₂O₃-LDHs/soft PVC composites are better than that of the soft PVC, but decline gradually with the increasing of mass fraction of Sb₂O₃-LDHs owing to the interface difference between Sb₂O₃ and the polymer matrix.