Abstract: Al(H₂PO₂)₃ was introduced to prepare a series of Al(H₂PO₂)₃/thermoplastic polyurethane composites (Al(H₂PO₂)₃/TPU) by melting blending technology. The flame retardancy and thermal stability of Al(H₂PO₂)₃/TPU composites were respectively investigated by limiting oxygen index (LOI), vertical burning test (UL-94), cone calorimeter, TG and SEM, the mechanical test was applied to research the effect of Al(H₂PO₂)₃ content on the mechanical properties of Al(H₂PO₂)₃/TPU composites. Flame retardancy results show that Al(H₂PO₂)₃ can effectively enhance the flame retardancy of Al(H₂PO₂)₃/TPU composites. 20wt% Al(H₂PO₂)₃ makes Al(H₂PO₂)₃/TPU composites UL-94 reach V-0 rating with LOI of 30.5vol%. TG test reveals that loading of Al(H₂PO₂)₃ will decrease the decomposition temperature of the composites while significantly enhance the char residue of Al(H₂PO₂)₃/TPU composites. The cone calorimeter results show that Al(H₂PO₂)₃ can significantly decrease the peak of heat release rate (pHRR) and total heat release (THR) of Al(H₂PO₂)₃/TPU composites, and increase the fire safety of the composites. pHRR and THR values of Al(H₂PO₂)₃/TPU composites with 20wt% Al(H₂PO₂)₃ loading are decreased 65.7% and 20.2% respectively compared with virgin TPU. SEM test indicates that char residue of Al(H₂PO₂)₃/TPU composites are significantly enhanced. TGA-FTIR was used to investigate flame retardant mechanism of Al(H₂PO₂)₃/TPU composites, which indicates that Al(H₂PO₂)₃ could promote the char formation of volatilized products of TPU molecular in combustion process, and reduce the production of combustible gas and enhance the flame retardancy of Al(H₂PO₂)₃/TPU composites.