Hexakis (4-formyl-2-methoxyphenoxy)-cyclotriphosphazene (I) was prepared by hexachlorocyclotriphosphazene and 4-hydroxy-3-methoxy-benzaldehyde. Hexakis (4-formyl -2 -methoxy-phenoxy)-cyclotriphosphazene (I) then reacted with substituted hydrazides to give hexakis(4- acylhydrazone-2-methoxyphenoxy)-cyclotriphosphazene ( IIa - IIg). The structures of IIa – IIg were confirmed by elementary analyses, IR, 1H NMR, 13C NMR, and MS spectra. Fire- resistant ABS resin were prepared by compound IIa – IIg and ABS resin, and the limited oxygen index (LOI) and UL 94 were tested. The results showed that they exhibited flame retardant effect, especially IIe, IIf exhibited a significant flame retardant effect.