Abstract: Hydroxystannate is a novel flame retardant aroused in recent years. In this study, starting from the flame retardant design, submicron calcium hydroxystannate (CSH) cubes were synthesized by chemical co-precipitation method, and then were rapidly in-situ coated by hydroxyapatite (HA) in simulated body fluid with high concentrations. Finally, the hybrid CSH@HA micro-nano particles were prepared and applied to the flame retardant flexible polyvinyl chloride (PVC). The results show that CSH@HA exhibits excellent flame retardancy on PVC. A very small amount of CSH@HA can significantly increase the limit oxygen index (LOI) value, and reduce the heat release rate, total heat release, total smoke release and CO production during combustion of PVC. By reacting with HCl generated during the degradation of PVC, CSH@HA protects the inner CSH and promotes more PVC into stable chars. The low loading of CSH@HA also improves the toughness of PVC while maintaining the mechanical properties. The CSH@HA hybrid flame retardant obtained in this paper pave a new way to the development of novel flame retardants.