Abstract: Hexaphenoxycyclotriphosphazene (HPCP) was synthesized by using Hexachlorocyclotriphosphazene (HCCP), phenol and sodium hydride as raw materials, with K2CO3 as catalyst and acetone as solvent. The product was characterized by FTIR, 1H NMR, 13C NMR, 31P NMR, DSC, TGA. HPCP was applied in acrylic resin as flame retardant and the effect of HPCP’s content on the thermal and flame-retardant properties was investigaged. The results showed that when the addition of 20 wt % HPCP, the acrylic resin could pass UL-94 V-0 classification and its limiting oxygen index (LOI) value was increased from 17.5 % to 32.2 %, and the residual mass up to 18.95 % in air at 700 ℃, mean heat release rate (Mean HRR) and total heat release (THR) were reduced to 43 kW/m2 and 42 MJ/m2, respectively.