A phosphorous flame retardant primarily includes hexachlorotriphosphazene (HCP) having poly(oxyalkylene)amine substitutes. The poly(oxyalkylene)amine includes at least two end groups. The phosphorous flame retardant can further include layered silicate clay. The layered silicate clay can be intercalated and modified with the poly(oxyalkylene)amine substitutes of HCP to effectively promote thermal stability. The flame retardant, phosphazene-poly(oxyalkylene)amine adducts, can be applied to a polymer. By the cross-linking between them, the flame-retarding property of the polymer can be improved. Also provided is a method for producing the flame retardant of phosphazene-poly(oxyalkylene)amine adducts and application thereof to a polymer.