To develop a novel hybrid organic-inorganic flame retardant and smoke suppressant, strontium hydroxystannate (SrSn(OH)₆) nanorods were synthesized via a co-precipitation method, and then the SrSn(OH)₆ were encapsulated by cyclomatrixpolyphosphazene (PZS) to prepare a novel core-shell organic-inorganic hybrid nano-flame retardant (PZS@SrSn(OH)₆). The micromorphology and chemical structure were analyzed by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and fourier transform infrared spectroscopy (FT-IR). The thermal degradation of PZS@SrSn(OH)₆ and EP/PZS@SrSn(OH)₆ composites was investigated by thermogravimetry analysis (TGA). The flame retardancy properties were studied by limited oxygen index (LOI) and CONE calorimetry tests. The flame retardant mechanism was determined by X-ray diffraction (XRD), SEM, energy-dispersive X-ray spectroscopy (EDS), and FT-IR. The results showed that PZS@SrSn(OH)₆ exhibited high flame retardant and smoke suppression efficiency. Significant synergy between PZS and SrSn(OH)₆ was found to enhance the flame retardancy of EP compared with pure EP, the LOI value was increased from 26.2% to 29.6% with 3wt% addition of PZS@SrSn(OH)₆. CONE calorimetry tests indicated that 3% incorporation of PZS@SrSn(OH)₆ brought about 29% and 37% maximum reduction in peak heat release rate and peak smoke production rate, and 242% improvement of char residue, respectively. A dense char structure is formed after combustion under elevated temperature for PZS@SrSn(OH)₆, and the char layer blocks the exchange between the decomposed fragments and oxygen, then protect EP matrix and improve the flame retardancy.