The present invention relates to a phosphazene compound, a composition comprising the phosphazene compound, a flame retardant comprising same, and the use thereof. The crystal form of a cyclotriphosphazene derivative flame retardant synthesized according to the present invention is the most stable crystal form, and same has a good heat stability and a high flame retardant efficiency; moreover, materials, whether engineering plastics or general-purpose plastics, as well as lithium ion battery electrolyte solutions, flame retardant fabrics and flame retardant papers, to which the crystal type cyclotriphosphazene derivative flame retardant synthesized according to the present invention has been added, are provided with an excellent flame retardant performance, a stable crystal form, and drip resistance, and only an extremely small addition amount is required to allow the flame retardant performance of a material to achieve V-0 standards, while the impact on the other properties of the material is relatively small.