The invention discloses a flame-retardant car roof material and a preparation method thereof. The flame-retardant car roof material is prepared by the following ingredients in parts by weight: 36-40 parts of polypropylene, 20-30 parts of trimethylol propane trimethyl acrylate, 20-30 parts of hydroxy propyl methyl cellulose, 15-20 parts of EPDM, 8-12 parts of polyvinyl alcohol, 3-5 parts of ammonium polyphosphate, 2-5 parts of 1,2-hydrindene, 2-3 parts of alundum powder and 2-5 parts of a flame retardant. The invention also provides a preparation method of the flame-retardant car roof material. The method mainly comprises the steps of placing a weighed raw material into a homogenizer to be uniformly mixed, feeding the mixed material into a double-screw extruder, cutting the mixed material through a screw, extruding and pelletizating.